Process for the preparation of 2′-O-alkyl-guanosine, cytidine, and uridine phosphoramidites

ABSTRACT

Processes for preparing 2′-O-alkylated guanosine, uridine, cytidine, and 2,6-diaminopurine 3′-O-phosphoramidites include the steps of alkylating nucleoside precursors, adding suitable blocking groups and phosphitylating. For the guanosine 2′-O-alkylated 3′-O-phosphoramidites, alkylation is effected on 2,6-diamino-9-(β-D-ribofuranosyl) purine followed by deamination. For uridine 2′-O-alkylated 3′-O-phosphoramidites, alkylation is effect on a dialkyl stannylene derivative of uridine. For cytidine 2′-O-alkylated 3′-O-phosphoramidites, alkylation is effected directly on cytidine. Alkylation is effected directly upon 2,6-diaminopurine.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.09/165,680, filed Oct. 2, 1998, now U.S. Pat. No. 6,133,438, which is adivisional of U.S. application Ser. No. 08/888,880, filed Jul. 7, 1997,now U.S. Pat. No. 5,856,466, which is a divisional of U.S. applicationSer. No. 08/410,002, filed Mar. 23, 1995, now U.S. Pat. No. 5,646,265,which is a continuation of U.S. application Ser. No. 07/968,849, filedOct. 30, 1992, now abandoned, which is a continuation-in-part of U.S.application Ser. No. 07/967,267, filed Oct. 27, 1992, which is acontinuation-in-part of U.S. application Ser. No. 07/918,362, filed Jul.23, 1992, now U.S. Pat. No. 5,506,351, and a continuation-in-part ofU.S. application Ser. No. 07/854,634, filed as the national stage entryof PCT application Ser. No. PCT/US91/00243, filed Jan. 11, 1991, nowabandoned, which is a continuation-in-part of Ser. No. 07/463,358 filedJan. 11, 1990, now abandoned, which is a continuation-in-part of U.S.application Ser. No. 07/566,977, filed Aug. 13, 1990, now abandoned.

FIELD OF INVENTION

This application is directed to processes for the preparation of2′-O-alkyl guanosine, uridine and cytidine phosphoramidites.

BACKGROUND OF THE INVENTION

A number of oligonucleotide analogs have been made. One class ofoligonucleotides that have been synthesized are the 2′-O-substitutedoligonucleotides. Such oligonucleotides have certain unique and usefulproperties. In U.S. patent application Ser. No. 07/814,961, filed Dec.24, 1991, abandoned entitled Gapped 2′ Modified PhospharothioateOligonucleotides, assigned to the same assignee as this application, theentire contents of which are herein incorporated by reference, 2′substituted nucleotides are introduced within an oligonucleotide toinduce increased binding of the oligonucleotide to a complementarytarget strand while allowing expression of RNase H activity to destroythe targeted strand.

In a recent article, Sproat, B. S., Beijer, B. and Iribarren, A.,Nucleic Acids Research, 1990, 18:41, the authors noted further use of2′-O-methyl substituted oligonucleotides as “valuable antisense probesfor studying pre-mRNA splicing and the structure of spliceosomes”.

2′-O-Methyl and ethyl nucleotides have been reported by a number ofauthors. Robins, et al., J. Org. Chem., 1974, 39, 1891; Cotten, et al.,Nucleic Acids Research, 1991, 19, 2629; Singer, et al., Biochemistry1976, 15, 5052; Robins, Can. J. Chem. 1981, 59, 3360; Inoue, et al.,Nucleic Acids Research, 1987, 15, 6131; and Wagner, et al., NucleicAcids Research, 1991, 19, 5965;112.

Sproat, B. S. and Lamond, A. I., in “2′-O-Methyloligoribonucleotides:synthesis and applications, Oligonucleotides and Analogs A PracticalApproach; Eckstein, F. Ed.; IRL Prest, Oxford, 1991, describe synthesesof 2′-O-methylribonucleoside-3′-O-phosphoramidites. The uridinephosphoramidite synthesis described therein requires both base and sugarprotection of the starting nucleoside prior to alkylation. Only afterthe base and sugar protecting groups are in place on the uridine is itthen alkylated. Post alkylation, the base protecting group is removedfollowed by 5′-O-dimethoxytritylation and phosphitylation. The cytidinephosphoramidite synthesis described by Sproat and Lamond utilizes (andthus requires) the base and sugar blocked 2′-O-methyl uridine analog.This analog is then converted to a blocked cytidine analog, the blockinggroup is removed from the sugar, the analog is dimethoxytritylated andfinally phosphitylated. The guanosine phosphoramidite synthesis taughtby Sproat and Lamond starts from a 2-amino-6-chloronucleoside having 3′and 5′ sugar hydroxy groups blocked. This nucleoside is converted to a2,6-dichloro derivative. The dichloro compound is then 2′-O alkylated.Following O-alkylation, the dichloro compound is converted to a diazidointermediate. The diazido intermediate is in turn converted to a diaminointermediate. The diamino intermediate is then deaminated to theguanosine analogue. The 2-amino group of the guanosine analogue isblocked followed by dimethoxytritylation and finally phosphitylation.This guanosine procedure is also published in Sproat, et. al., NucleicAcids Research, 1991 19:733.

The above synthetic procedures involve multiple steps and numerousreagent treatments—9 different reagent treatments for uridine, 10 forcytidine and 12 for guanosine. For the cytidine and guanosine compoundsat least one of the reagents that is required is not readily availableand thus is a very expensive reagent.

Certain oligonucleotides containing 2′-O-alkyl substituted nucleotidesare promising candidates for use as human pharmaceuticals. For use inlarge scale therapeutic testing and eventually for human pharmaceuticaluse, large amounts of these oligonucleotides must be synthesized. Thelarge amounts of oligonucleotides in turn requires large amounts of the2′-O-alkyl nucleoside phosphoramidites used in synthesizing theoligonucleotides. Consideration must therefore be given to both cost andpurity of the starting phosphoramidites used in the synthesis of sucholigonucleotides. As a general premise, as the number of synthetic stepsincreases, the cost of manufacture increases. Further as the number ofsteps increases, quality control problems escalate. In view of this, itis evident that there is a great need for new and improved proceduresfor preparing nucleoside phosphoramidites.

OBJECTS OF THE INVENTION

It is an object of this invention to provide new and improved syntheticmethods for the preparation of 2′-substituted nucleosidephosphoramidites.

It is a further object of this invention to provide new and improvedsynthetic methods for the preparation of 2′-O-alkyl nucleosidephosphoramidites.

A further object of this invention is to provide new and improvedsyntheses of 2′-O-alkyl guanosine phosphoramidites.

A further object of this invention is to provide new and improvedsyntheses of 2′-O-alkyl cytidine phosphoramidites.

A further object of this invention is to provide new and improvedsyntheses of 2′-O-alkyl uridine phosphoramidites.

A further object of this invention is to provide new and improvedsyntheses of 2,6-diamino-9-(2′-O-alkyl-β-D-ribofuranosyl)purinephosphoramidites.

A further object of this invention is to provide new and improvedoligonucleotide syntheses that utilize the improved phosphoramiditesyntheses of the invention.

These and other objects will become apparent to persons of ordinaryskill in the art from a review of the present specification and appendedclaims.

SUMMARY OF THE INVENTION

Previous methods for the preparation of 2′-O-alkylated nucleosidephosphoramidites involved numerous steps and reagents, resulting indecreased efficiency and increased cost.

In accordance with this invention there are provided improved processesfor the preparation of 2′-O-alkylated nucleoside phosphoramiditesincluding 2′-O-alkylated guanosine, cytidine and uridinephosphoramidites. Further in accordance with this invention there areprovided processes for the preparation of oligonucleotides that includeat least one 2′-O-alkylated nucleotide incorporated within theoligonucleotide.

In accordance with the invention there are provided processes forpreparing a 2′-O-alkylated guanosine 3′-O-phosphoramidite comprising thesteps of alkylating a 2,6-diamino-9-(ribofuranosyl)purine to form a2,6-diamino-9-(2′-O-alkylated ribofuranosyl)purine; deaminating said2,6-diamino-9-(2′-O-alkylated ribofuranosyl)purine to form a2′-O-alkylated guanosine; blocking the 5′-hydroxyl moiety of said2′-O-alkylated guanosine; and phosphitylating the 3′-position of said5′-blocked 2′-O-alkylated guanosine.

Further in accordance with the invention there are provided processesfor preparing a 2′-O-alkylated cytidine 3′-phosphoramidite that includethe steps of alkylating an unblocked cytidine to form a 2′-O-alkylatedcytidine; blocking the 5′-hydroxyl moiety of said 2′-O-alkylatedcytidine; and phosphitylating the 3′-position of said 5′-blocked2′-O-alkylated cytidine.

Further in accordance with the invention there are provided processesfor preparing a 2′-O-alkylated uridine 3′-O-phosphoramidite that includethe steps of treating a uridine with a dialkyltin oxide to form a2′,3′-O-dialkylstannylene derivative of uridine; alkylating saidstannylene derivative of uridine to form a 2′-O-alkylated uridine;blocking the 5′-hydroxyl moiety of said 2′-O-alkylated uridine; andphosphitylating the 3′-position of said 5′-blocked 2′-O-alkylateduridine.

Further in accordance with the invention there are provided processesfor preparing a 2′-O-alkylated 2,6-diamino-9-(β-D-ribofuranosyl)purine3′-O-phosphoramidite that include the steps of alkylating a2,6-diamino-9-(β-D-ribofuranosyl)-2′-purine to provide a 2′-O-alkylated2,6-diamino-9-(β-D-ribofuranosyl)purine; blocking the 5′-hydroxyl moietyof said 2′-O-alkylated 2,6-diamino-9-(β-D-ribofuranosyl)purine; andphosphitylating the 3′-position of said 5′-blocked 2′-O-alkylated2,6-diamino-9-(β-D-ribofuranosyl)purine.

Further in accordance with the invention there are provided processesfor preparing an oligonucleotide that include at least one2′-O-alkylated guanosine nucleotide within the oligonucleotide, theprocesses comprise the steps of alkylating a2,6-diamino-9-(ribofuranosyl)purine to form a2,6-diamino-9-(2′-O-alkylated ribofuranosyl)purine; deaminating said2,6-diamino-9-(2′-O-alkylated ribofuranosyl)purine to form a2′-O-alkylated guanosine; blocking the 5′-hydroxyl moiety of said2′-O-alkylated guanosine; phosphitylating the 3′-position of said5′-blocked 2′-O-alkylated guanosine to form a 2′-O-alkylated guanosine3′-O-phosphoramidite; and coupling, utilizing phosphoramidite couplingconditions, said 2′-O-alkylated guanosine 3′-O-phosphoramidite to a5′-hydroxyl moiety of an oligonucleotide.

Further in accordance with the invention there are provided processesfor preparing an oligonucleotide that include at least one2′-O-alkylated cytidine nucleotide within the sequence of theoligonucleotide, the processes comprise the steps of alkylating acytidine to provide a 2′-O-alkylated cytidine; blocking the 5′-hydroxylmoiety of said 2′-O-alkylated cytidine; phosphitylating the 3′-positionof said 5′-blocked 2′-O-alkylated cytidine to form a 2′-O-alkylatedcytidine 3′-O-phosphoramidite; and coupling, utilizing phosphoramiditecoupling chemistry, said 2′-O-alkylated cytidine 3′-phosphoramidite to a5′-hydroxyl moiety of an oligonucleotide.

Further in accordance with the invention there are provided processesfor preparing an oligonucleotide that include at least one2′-O-alkylated uridine nucleotide within the sequence of theoligonucleotide, the processes comprise the steps of treating uridinewith a dialkyltin oxide to form a 2′,3′-O-dialkylstannylene derivativeof uridine; alkylating said stannylene derivative to provide a2′-O-alkylated uridine; blocking the 5′-hydroxyl moiety of said2′-O-alkylated uridine; phosphitylating the 3′-position of said5′-blocked 2′-O-alkylated uridine to form a 2′-O-alkylated uridine3′-O-phosphoramidite; and coupling, utilizing phosphoramidite chemistry,said 2′-O-alkylated uridine 3′-O-phosphoramidite to a 5′-hydroxyl moietyof an oligonucleotide.

Further in accordance with the invention there are provided processesfor preparing an oligonucleotide that include at least one2′-O-alkylated 2,6-diamino-9-(β-D-ribofuranosyl)purine nucleotide withinthe sequence of the oligonucleotide, the processes comprise the steps ofalkylating a 2,6-diamino-9-(β-D-ribofuranosyl)purine to provide a2′-O-alkylated 2,6-diamino-9-(β-D-ribofuranosyl)purine; blocking the5′-hydroxyl moiety of said 2′-O-alkylated2,6-diamino-9-(β-D-ribofuranosyl)purine; phosphitylating the 3′-positionof said 5′-blocked 2′-O-alkylated2,6-diamino-9-(β-D-ribofuranosyl)purine to form a 2′-O-alkylated2,6-diamino-9-(β-D-ribofuranosyl)purine 3′-O-phosphoramidite; andcoupling, utilizing phosphoramidite chemistry, said 2′-O-alkylated2,6-diamino-9-(β-D-ribofuranosyl)purine 3′-O-phosphoramidite to a5′-hydroxyl moiety of an oligonucleotide.

In the context of this invention, the term “nucleoside” refers to asugar and a base that are joined together, normally about an “anomeric”carbon on the sugar. Both α and β sugars are encompassed by the presentinvention. In preferred embodiments of the present invention thenucleoside sugar is a pentofuranosyl sugar, however, other sugars mightalso be utilized such as carbocyclic or 4′-deoxy-4′-thio sugar analogs.

The term “oligonucleotide” refers to polynucleotides formed from aplurality of nucleoside units that are joined by phosphorous linkages.These phosphorous linkages included phosphodiester linkages,phosphorothioate linkages, phosphotriester linkages andalkylphosphonates, all of which can be synthesized via phosphoramiditecoupling chemistry, and phosphorodithioate linkages, which can besynthesized via phosphorothioamidite coupling chemistry. Othermodifications consistent with the spirit of this invention are alsodeemed to be within the scope of the invention.

Further as used in this invention, the term “alkylating” refers to theaddition of an alkyl, alkenyl or alkynyl moiety, preferably an alkylmoiety, to the precursors of the nucleosides phosphoramidites of theinvention. Alkylation of the 2′ position of the nucleoside sugar linksthe alkylating moiety to the 2′ position of the sugar via an etherlinkage.

Preferred alkyl moieties include un-substituted and substituted straightchain C₁-C₂₀ alkyl and un-substituted and substituted branch chainC₁-C₂₀ alkyl. Preferred alkenyl groups include un-substituted andsubstituted straight chain C₂-C₂₀ alkenyl, and un-substituted andsubstituted branch chain C₂-C₂₀ alkenyl. Preferred alkynyl groupsinclude un-substituted and substituted straight chain C₂-C₂₀ alkynyl andun-substituted and substituted branch chain C₂-C₂₀ alkynyl. Thuspreferred alkylation groups include but are not limited to C₁ to C₂₀straight or branched chain lower alkyl or substituted lower alkyl, C₂ toC₂₀ straight or branched chain lower alkenyl or substituted loweralkynyl, C₂ to C₂₀ straight or branched chain lower alkynyl orsubstituted lower alkynyl.

Alkyl groups of the invention include but are not limited to C₁-C₂₀straight and branched chained alkyls such as methyl, ethyl, propyl,butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, hexadecyl, octadecyl, nonadecyl andeicosyl, isopropyl, 2-butyl, isobutyl, 2-methylbutyl, isopentyl,2-methyl-pentyl, 3-methylpentyl, 2-ethylhexyl and 2-propyL pentyl.Alkenyl groups include, but are not limited to, unsaturated moietiesderived from the above alkyl groups including, but not limited to,vinyl, allyl and crotyl. Alkynyl groups include unsaturated moietieshaving at least one triple bond that are derived from the above alkylgroups including, but not limited to, ethynyl and propargyl.

Substituent groups for the above include, but are not limited to, alkylgroups, alkenyl groups, and alkynyl groups such as alicyclic alkyl,alicyclic alkenyl, alicyclic alkynyl, haloalkyl, haloalkenyl,haloalkynyl, alkoxy, thioalkoxy, haloalkoxy, carbocyclic, heterocyclicand aryl groups as well as halogen, hydroxyl, amino, azido, carboxy,cyano, nitro, mercapto, sulfide; sulfone and sulfoxide groups. Othersuitable substituent groups include steroids, reporter groups, reporterenzymes, lipophilic molecules, peptides, protein, vitamins, RNA cleavingcomplexes, metal chelators, alkylators, intercalators, cross-linkingagents, rhodamines, coumarins, acridones, pyrenes, stilbenes,oxazolo-pyridocarbazoles, anthraquinones, phenanthridines, phenazines,azidobenzenes, psoralens, porphyrins, cholic acids, folic acids andcholesterols. Aryl groups include but are not limited to phenyl, tolyl,benzyl, naphthyl, anthracyl, phenanthryl, pyrenyl, and xylyl. Halogensinclude fluorine, chlorine and bromine. Suitable heterocyclic groupsinclude but are not limited to imidazole, tetrazole, triazole,pyrrolidine, piperidine, piperazine and morpholine. Amines includeamines of all of the above alkyl, alkenyl, alkynyl and aryl groupsincluding primary and secondary amines and “masked amines” suc:h asphthalimide. Amines are also meant to include polyalkylamino compoundsand aminoalkylamines such as aminopropylamine and furtherheterocyclo-alkylamines such as imidazol-1, 2 or 4-yl-propylamine. RNAcleaving complexes may be, for example, intercalators or groups whichbind in the minor groove of RNA. Intercalators are molecules whichinsert themselves between neighboring bases of an olignoucleotide. Awell known intercalator is acridine. Reporter molecules are moleculeswhich may aid in the identification of a molecule, either visually orotherwise. For example, biotin and various fluorophores are effectivereporter groups. Cross-linking agents effectively join two groups. Somecross-linking agents are commercially available such as biotin or3′-maleimidobenzoyl-N-hydroxy-succinimide available from BoeringerMannheim (Indianapolis, Ind.).

In accordance with methods of the present invention,, the alkylation ispreferably conducted in the presence of a base, preferably a metalhydride such as sodium hydride. Alkylation of the2′,3′-O-dialkylstannylene derivative of uridine preferably is performedin the presence of a salt such as a metal halide. Cesium flouride andsodium iodide are preferred in some embodiments of the presentinvention. Additionally, the 5′ hydroxyl blocking group is preferably adimethoxytrityl moiety. The phosphitylating reagent is preferablybis-N,N-diisopropylaminocyanoethylphosphite and the phosphitylatingreaction is preferably conducted in the presence ofN,N-diisopropylamino-hydrotetrazolide.

In effecting the alkylation of uridine, 2′,3′-O-(dibutylstannylene)uridine is alkylated. The dibutylstannylene derivative in turn wasprepared in one step from uridine by reaction with dibutyl tin oxideutilizing the procedure of by Wagner, D. , Verheyden, J. P. H. andMoffat, J. G., J. Org. Chem. 1974, 39:24. As noted by these authors,2′,3′-di-O-(dibutylstannylene) nucleosides are activated towardsalkylation. By using the dibutylstannylene derivative alkylation of thesugar hydroxyls was effected without concurrent alkylation of the uracilbase. The dibutylstannylene group thus served as a activating group nota blocking group.

For the synthesis ofN4-benzoyl-5′-O-(4,4′-dimethoxytriphenylmethyl)-2′-O-methyl cytidine3′-O-β-cyanoethyl-N,N-diisopropylaminophosphoramidite two methods forthe preparation of the intermediate N4-benzoyl-2′-O-methylcytidine arecompared. Method A involves blocking of the 3′-5′ sites with the TIPS-Clreagent to allow methylation only on the 2′ position. Method B, apreferred method of the invention, uses a direct methylation of cytidinefollowed by separation of the resulting mixture of 2′ and 3′ isomers.The overall yields are comparable. In using Method B, the 2′-O-isomercan be crystallized out from the mixture, filtered and the remainingmother liquors taken through the dimethoxytritylation step prior toseparation of the 2′ and 3′ isomers or alternately the totality of thealkylated cytidine can be taken through the dimethoxytritylation stepwith separation of the 2′ isomer only effected after this step.

In effecting the alkylation of guanosine, 2′,6 diaminopurine isalkylated, for example, by methods described in U.S. application Ser.No. 07/967,267 filed Oct. 27, 1992.

The amino moiety of the phosphoramidites of the invention can beselected from various amines presently used for such phosphoramidites.Such amines include both aliphatic and heteroaryl amines as aredescribed in various United States patents, principally those to M.Caruthers and associates. These include U.S. Pat. Nos. 4,668,777, issuedMay 26, 1987; 4,458,066, issued Jul. 3, 1984; 4,415,732, issued Nov. 15,1983; and 4,500,707, issued Feb. 19, 1985, all of which are hereinincorporated by reference. One preferred amino group isdiisopropylamino.

In addition to the amino moiety of the phosphoramidite, forphosphodiester and phosphorothioate linkages, an additional phosphorousblocking group is used. One preferred blocking group is the cyanoethylgroup. Other phosphorous blocking groups include methoxy and2-(methylsulphonyl)ethyl. Additionally an activating agent is normallyused for the phosphoramidits coupling chemistry. One preferredactivating agent is N,N-diisopropylaminohydrotetrazolide. Other suitablemoieties for these functions are also disclosed in the above notedpatents as well as in U.S. Pat. No. 4,725,677, issued Feb. 16, 1988 andBerner, S., Muhlegger, K., and Seliger, H., Nucleic Acids Research 1989,17:853; Dahl, B. H., Nielsen, J. and Dahl, O., Nucleic Acid; Research1987, 15:1729; and Nielson, J. Marugg, J. E., Van Boom, J. H., Honnens,J., Taagaard, M. and Dahl, O., J. Chem. Research 1986, 26, all of whichare herein incorporated by reference.

For use in phosphorothioate linkage, the Beaucage reagent is describedin Beaucage, S. L. and Caruthers, M. H., Tetrahedron Letters 1981,22:1859 as well as in Zon, G. and Stec, J., Phosphorothioateoligonucleotides: Oligonucleotides and Analogs A Practical Approach;Eckstein, F. Ed.; IRL Press, Oxford, 1991, which also describessulfurization by elemental sulfur.

EXAMPLES

The following examples illustrate the invention, however, they are notintended as being limiting. In various examples the nomenclature4,4′-dimethoxytriphenylmethyl and dimethoxytrityl are usedinterchangeably to reference the DMT blocking group positioned on the5′-hydroxyl moiety of the various nucleoside and nucleotides of theinvention.

NMR spectra were obtained with the following instruments: ¹H-NMR: VarianGemini-200 (199.975 MHz), ¹³C-NMR: Varian Gemini-200 (50.289 MHz). NMRspectra were recorded using either deuteriochloroform (tetramethylsilaneas internal standard) or dimethylsulfoxide-d₆ as solvent. The followingabbreviations were used to designate the multiplicity of individualsignals: s=singlet, d=doublet, t=triplet, q=quartet, ABq=ab quartet,m=multiplet, dd=doublet of doublets, br s=broad singlet. Mass spectrawere acquired on a VG 70-SEQ instrument (VG Analytical (Fisons)), usingfast atom bombardment ionization (7 kV Xe atoms). Solvent ratios forcolumn chromatography are given as volume/volume. Evaporations ofsolvents were performed in vacuo (60 torr) at 30° C. unless otherwisespecified. Melting points are reported uncorrected.

Example 1 2,6-Diamino-9-(β-D-ribofuranosyl)purine

In accordance with modifications of the procedures described in Robins,M. J., Hanske, F. and Beriner, S. E., Can. J. Chem., 59:3360 (1981),guanosine hydrate (49 g, Aldrich Chemical Co.), toluene (200 ml),hexamethyldisilazane (160 ml, 4.3 eq) and trifluoromethanesulfonic acid(3.7 ml) were loaded in a stainless steel Parr bomb. The bomb was sealedand heated approximately ⅓ submerged in an oil bath at 170° C. for 5days. The bomb was cooled in a dry ice acetone bath and opened. Thecontents were transferred to a 2 liter round bottom flask using methanol(MeOH) and the solvent evaporated on a Buchii evaporator. 1:1 H₂O/MeOH(600 ml) was added to the residue and the resulting brown suspension wasrefluxed 4-5 hr. The resulting suspension was evaporated on the Buchiievaporator to remove the methanol (≈½ volume). Additional H₂O (≈300 ml)was added and the mixture was heated, treated with charcoal and filteredthrough a Celite filter pad. Upon cooling, a crystalline solid formed.The solid was isolated by filtration, washed with H₂O and dried underhigh vacuum at 90° C. to yield the product (43.7 g, 89% yield) as a tansolid. UV and NMR spectra of this compound compared to literaturevalues.

This variation of the procedures of Robins, et al. supra, eliminated theneed to utilize liquid ammonia in the reaction mixture since the ammoniamolecule is generated in situ from the silazane reagent and the water ofhydration of the guanosine hydrate starting material. Further, the useof chlorotrimethylsilane was not necessary nor was it necessary toconduct the reaction under anhydrous conditions, do a preliminaryevaporation, or open and re-seal the Parr bomb under a dry nitrogenatmosphere.

Example 2 2,6-Diamino-9-(2′-O-propyl-β-D-ribofuranosyl)purine &2,6-Diamino-9-(3-O-propyl-β-D-ribofuranosyl)purine

Sodium hydride (NaH) (2.1 g) was added to2,6-diamino-9-(β-D-ribofuranosyl) purine (10.5 g) in drydimethylformamide (DMF) (150 ml). After stirring for 10 min, iodopropane(6 ml) was added. The solution was stirred for 45 min at roomtemperature followed by the addition of a further aliquot of NaH (600mg). The reaction mixture was stirred overnight and then quenched by theaddition of ethanol (EtOH) (5 ml). The reaction mixture was evaporatedin vacuo, the residue suspended in 10% MeOH/CH₂Cl₂ and purified bysilica gel chromatography (300 g) using 5→10% MeOH/CH₂Cl₂ as the eluent.The 2′,3′-di-O-propyl product eluted first followed by the 2′-O-propylproduct and then the 3′-O-propyl product. The 2′-O-propyl productcontaining fractions were pooled and the solvent stripped to yield acrude foam. The foam was crystallized from H₂O (40 ml), washed with coldH₂O and dried to yield 2.9 g of the 2′-O-propyl compound. The motherliquor was evaporated, re-chromatographed and crystallized to yield anadditional 2.4 g of the 2′-O-propyl compound. The second mother liquorwas evaporated to yield 4 g of a mixture of 2′ and 3′-O-propyl compoundsas an oil. Fractions containing the 3′-O-propyl product as the majorproduct were evaporated and residue crystallized from water. (SeeExample 17 below for isolation and characterization of the2′,3′-di-O-propyl compound).

2,6-Diamino-9-(2′-O-propyl-β-D-ribofuranosyl)purine

¹H NMR (DMSO-d₆) δ 0.76 (t, 3, CH₃), 1.4 (tq, 2, CH₂), 3.3 (m, 1,H-5″+HDO), 3.65-3.45 (m, 3, H-5′, O—CH₂), 3.9 (m, 1), 4.25 (br m, 1),4.38 (dd, 1), 5.1 (br d, 1 3′—OH), 5.45 (br t, 1, 5′—OH), 5.75 (br s, 2,6—NH₂), 5.83 (d, 1, H-1′), 6.77 (b:r s, 2, 2—NH₂) and 7.95 (s, 1, H-8).Anal. Calcd. for C₁₃H₂₀N₆O₄.½H₂O: C, 46.91; H, 6.2; N, 25.25. Found: C,47.09; H, 6.37; N, 25.33.

2,6-Diamino-9-(3-O-propyl-β-D-ribofuranosyl)purine

¹H NMR (DMSO-₆) δ 0.75 (t, 3, CH₃), 1.4 (tq, 2, CH₂), 3.27-3.5 (ABX 2,O—CH₂—), 3.5 and 3.6 (ABX, 2, H-5′), 3.9 (m,1), 4.22 (m, 1), 4.35 (m,1), 5.1 (br d, 1, 2′—OH), 5.45 (br t, 1, 5′—OH), 5.75 (br s, 2, 6—NH₂),5.8 (d, 1, H-1′), 6.8 (br 5, 2CH₂, 2—H2) and 7.95 (s, 1, H-8).

Example 3 2′-O-Propylguanosine

A mixture of 2,6-Diamino-9-(2′-O-propyl-β-D-ribofuranosyl) purine and2,6-Diamino-9-(3′-O-propyl-β-D-ribofuranosyl) purine (4.6 gm) andadenosine deaminase (200 mg, Sigma Chemicals Type II) were stirred atroom temperature overnight in 0.1 N tris buffer (150 ml, pH 7.4), DMSO(100 ml) and 0.1 N sodium phosphate buffer (10 ml). A further aliquot ofadenosine deaminase (140 mg) in 0.1 N phosphate buffer (30 ml) and DMSO(20 ml) was added and the reaction stirred an addition 24 hrs. Thesolvent was evaporated in vacuo and the residue flash chromatographed onsilica gel utilizing 5→20% MeOH/CH₂Cl₂. Product-containing fractionswere evaporated in vacuo and the residue crystallized from H₂O to yield2.6 gm of product. m.p. dec>270° C. ¹H NMR (DMSO-d₆) δ 0.75 (t, 3, CH₃),1.42 (tq, 2, CH₂), 3.3-3.6 (m, 4, H-5′, O—CH₂), 3,85 (m, 1), 4.2 (m, 1),4.23 (m, 1), 5.10 (t, 1, 5′—OH), 5.13 (d, 1, 3′—OH), 5.75 (d, 1, H-1′),6.45 (br s, 2, NH₂), 7.95 (s, 1, H-8) and 10.67 (br s, 1, NH). Anal.Calcd. for C₁₃H₁₉N₅O₅: C, 47.99; H, 5.89; N, 21.53. Found: C, 47.90, H,5.85; N, 21.44.

Example 4 N2-Isobutyryl-2′-O-propylguanosine

2′-O-Propylguanosine (3.6 gm) in pyridine (50 ml) was cooled in an icebath and trimethylsilyl chloride (8.4 ml, 6 eq.) was added. The reactionmixture was stirred for 30 min and isobutyryl chloride (5.8 ml, 5 eq.)was added. The solution was stirred for 4 hours during which it wasallowed to warm to room temperature. The solution was cooled, H₂O added(10 ml) and the solution was stirred for an additional 30 mins.Concentrated NH₄OH (10 ml) was added and the solution evaporated invacuo. The residue was purified by silica gel chromatography using 10%MeOH/CH₂Cl₂ to elute the product. Product-containing fractions wereevaporated to yield 2.5 g of product as a foam. An analytical sample wasre-chromatographed on silica and eluted with CH₂Cl₂→6% MeOH/CH₂Cl₂. ¹HNMR (DMSO-d₆) δ 0.75 (t, 3, CH₃), 1.13 [d, 6, CH(CH₃)₂], 1.4 (m, 2,CH₂), 2.75 [m, 1, CH(CH₃)₂], 3.52 (m, 6, OCH₂), 3.36 and 3.6 (ABX, 2,H-5′), 3.95 (m, 1), 4.26 (m, 1), 4.33 (m, 1), 5.07 (t, 1, 5′—OH), 5.18(d, 1, 3′—OH), 5.9 (d, 1, H-1′), 8.25 (s, 1, H-8), 11.65 (br s, 1, NH)and 12.1 (br s, 1, NH). Anal. Calcd. for CH₁₇H₂₅N₅O₆.½H₂O: C, 50.49; H,6.48; N, 17.32. Found: C, 50.81; H, 6.62; N, 17.04.

Example 5 N2-Isobutyryl-5′-dimethoxytrityl-2′-O-propylguanosine

N2-Isobutyryl-2′-O-propylguanosine (2.64 g) was co-evaporated withpyridine and then solubilized in pyridine (180 ml). Dimethoxytritylchloride (2.4 g, 1.1 eq) and dimethylaminopyridine (50 mg) were addedwith stirring at room temperature. The reaction mixture was stirredovernight and evaporated in vacuo. The residue was partitioned betweenCH₂Cl₂/2×dil Na₂CO₃. The organic phase was dried (MgSO₄) and evaporated.The residue was purified by silica gel chromatography (1:1 EtOAc/Hex→5%MeOH/EtOAc, 1% TEA) to yield 4.1 g of product. ¹H NMR (DMSO-d₆) δ 0.78(t, 3, CH₃), 1.12 [d, 6, CH(CH₃)₂], 1.46 (s, 2, CH₂), 2.75 [m, 1,CH(CH₃)₂], 3.35 and 3.55 (ABX, 2, H-5′), 3.73 (s, 6, OCH₂), 4.0 (s, 1),4.3 (m, 1), 4.4 (m, 1), 5.18 (d, 1, 3′—OH), 5.93 (d, 1, H-1′), 6.8, 7.2,7.36 (m, 13, DMTr), 8.13 (s, 1, H-8), 11.63 (br s, 1, NH) and 12.1 (brs, 1, NH). Anal. Calcd. for C₃₈H₄₂N₅O₈.H₂O: C, 63.83; H, 6.20; N, 9.80.Found: C, 64.22; H, 6.35; N, 9.55.

Example 6 N2-Isobutyryl-5′-dimethoxytrityl-2′-O-propylguanouine3′-β-cyanoethyl-N,N-diisopropylphosphoramidite

A CH₂Cl₂ solution ofN2-Isobutyryl-5′-dimethoxytrityl-2′-O-propylguanosine (4.1 g),bis-(N,N-diisopropylamino)-2-cyanoethylphosphite (3.7 ml, 2 eq) andN,N-diisopropylammonium tetrazolide (0.5 g, 0.5 eq) was stirred at roomtemperature overnight. The solution was partitioned against dil. Na₂CO₃and then dil. Na₂CO₃/NaCl and dried over MgSO₄. The solvent wasevaporated in and the residue was purified by silica gal chromatography(120 g, 1%TEA in EtOAc) to yield 5.2 g of product as a foam. ³¹NMR(CDCl₃) δ 150.5, 150.8.

Example 7 2,6-Diamino-9-(2′-O-pentyl-β-D-ribafuranosyl)purine2,6-Diamino-9-(3′-O-pentyl-β-D-ribofuranosyl)purine

2,6-Diamino-9-(β-D-ribofuranosyl)purine (10 g) was treated with sodiumhydride (1.7 g, 1.2 eq) and bromopentane (5.3 ml, 1.2 eq) in DMF (90 ml)as per the procedure of Example 2. Silica gel chromatography yieldedthree components. The first eluted component (not characterized butbelieved to be the 2,3-di-(O-pentyl) compound was isolated as an oil(700 mg). The next component isolated as a foam (3.3 g) was crystallizedfrom NeOH to yield 2.8 g of2,6-diamino-9-(2′-O-pentyl-β-D-ribofuranosyl)purine. The third componentisolated as a solid (200 mg) was crystallized from MeOH to yield 80 mgof 2,6-diamino-9-(3′-O-pentyl-β-D-ribofuranosyl)purine. Fractionscontaining mixtures of the first and second components were evaporatedand the residue crystallized from MeON to yield a further 900 mg of the2-O-pentyl compound. Further fraction yielded 1.2 g of a mixture of the2′-O-pentyl and 3′-O-pentyl compounds.

2,6-Diamino-9-(2′-O-pentyl-β-D-ribofuranosyl) purine

¹H NMR (DMSO-d₆) δ 0.75 (t, 3, CH₃), 1.16 (m, 4, CH₂), 1.39 (m, 2, CH₂),3.53 (m, 2, CH₂), 3.3 and 3.6 (ABX, 2, H-5′), 3.93 (br s, 1), 4.23 (m,1), 4.38 (m, 1), 5.1 (d, 1 3′—OH), 5.5 (t, 1, 5′—OH), 5.75 (br s, 2,6—NH₂), 5.82 (d, 1, H-1′), 6.8 (br s, 2, 2—NH₂) and 7.93 (s, 1, H-8).

2,6-Diamino-9-(3′-O-pentyl-β-D-ribofuranosyl)purine

¹H NMR (DMSO-d₆) δ 0.87 (t, 3, CH₃), 1.3 (m, 4, CH₂), 1.55 (m, 2, CU₂),3.5 (m, 2, O—CH₂—), 3.6 (m, 2, H-5′), 3.86 (m, 1), 3.95 (m, 1), 4.6 (m,1), 5.32 (br d, 1 2′—OH), 5.46 (br t, 1, 5′—OH), 5.70 (d, 1, H-1′), 5.75(br s, 2, 6—NH₂), 6.76 (br s, 2, 2—NH₂) and 7.93 (s, 1, H-8).

Example 8 2′-O-Pentylguanosine

2,6-diamino-9-(2′-O-pentyl-β-D-ribofuranosyl) purine (1.9 g) in 0.1 Msodium phosphate buffer (50 ml, pH 6.0) and DMSO (25 ml) was treatedwith adenosine deaminase (added in two aliquots—first aliquot 50 mg,second aliquot 80 mg) at 35° C. as per the procedure of Example 3 toyield 1.4 g of product. ¹H NMR (DMSO-d₆) δ 0.8 (t, 3, CH₃), 1.16 (a, 4,2x CH₂), 1.4 (m, 2, CH₂), 3.38, 3.6 (s, 4, OCH₂, H-5′), 3.93 (s, 1,H-4′), 4.28 (m, 2, H-2′, H-3′), 5.17 (br, 2, 5′, 3′—OH), 5.8 (d, 1,H-1′), 6.53 (br s, 2, NH₂), 8.0 (s, 1, H-8) and 10.68 (br, 1, NH).

Example 9 N2-Isobutyryl-2′-O-pentylquanosine

2′-O-pentylguanosine (2.3 g) in pyridine (35 ml) was treated withtrimethylsilyl chloride (4.15 ml, 5 eq) and isobutyryl chloride (3.4 ml,5 eq) as per the procedure of Example 4 to yield the product as a foam(2.3 g). An analytical sample was crystallized from EtOAc/Hex. m.p.178-180° C. ¹H NMR (DMSO-₆) δ 0.75 (t, 3, CH₃), 1.1 [m, 10, 2x CH₂,CH(Cl₃)₂], 1.4 (m, 2, CH₂), 2.74 [m, 1, CH(CH₃)₂], 3.56 (m, 4, OCH₂,H-5′), 3.93 (m, 1, H-4′), 4.25 (m, 1), 4.34 (s, 1), 5.05 (t, 1, 5′—OH),5.17 (d, 1, 3′—OH), 5.88 (d, 1, H-1′), 8.27 (s, 1, H-8), 11.65 (br s, 1,NH) and 12.05 (br s, 1, NH). Anal. Calcd. for C₁₉H₂₉N₅O₆: C, 53.89; H,6.90; N, 16.54. Found: 53.75; H. 6.92; N, 16.40

Example 10 N2-Isobutyryl-5′-dimethoxytrityl-2′-O-pentylguanosine

N2-Isobutyryl-2′-O-pentylguanosine (2.3 g) was treated withdimethoxytrityl chloride (1.7 g, 1.1 eq), and dimethylaminopyridine (100mg as a catalyst) in pyridine (50 ml) as per the procedure of Example 5to yield the product as a foam (2.9 g). ¹H NMR (DMSO-₆) δ 0.83 (t, 3,CH₃), 1.2 [m, 10, 2x CH₂, CH(CH₃)₂], 1.48 (m, 2, CH₂), 2.78 [m, 1,CH(CH₃)₂], 3.4, 3.6 (m, 4, OCH₂, H-5′), 3.75 (s, 6, OCH₃), 4.07 (m, 1),4.27 (m, 1), 4.42 (m, 1), 5.2 (br d, 1, 3′—OH), 5.95 (d, 1, H-1′), 6.85,7.25, 7.38 (m, 13, DMTr), 8.15 (s, 1, H-8), 11.67 (br s, 1, NH) and 12.1(br s, 1, NH). Anal. Calcd. for Anal. Calcd. for C₄₀H₄₇N₅O₈.½H₂O: C,65.38; H, 6.58; N, 9.53. Found: C, 65.37; H, 6.59; N, 9.39.

Example 11 N2-Isobutyryl-5′-dimethoxytrityl-2′-O-pentylquanosine3′-β-cyanoethyl-N,N-diisopropylphosphoramidite

N2-Isobutyryl-5′ -dimethoxytrityl-2′-O-pentyl-guanosine (1.7 g) wastreated with bis-(N,N-diisopropylamino)-2-cyanoethyl-phosphite (1.48 g)and N,N-diisopropylammonium tetrazolide (200 mg) as per the procedure ofExample 6 to yield the product (1.4 g). ³¹P NMR (CDCl₃) δ 150.5, 150.85.

Example 12 2,6-Diamino-9-(2′ O -nonyl-β-D-ribofuranosyl) purine

2,6-Diamino-9-(β-D-ribofuranosyl)purine (50 g, 180 mmol) was treatedwith sodium hydride (8.8 g, 220 mmol) and bromononane (59 g, 54.4 ml,285 mmol) in DMF (700 ml) as per the procedure of Example 2 (the diaminocompound in DMF was cooled in an ice bath during the addition of NaH) toyield 83 g of crude product. 50 g of crude product was purified bysilica gel chromatography. Fraction containing 2′-O-nonyl and 3′-O-nonylproduct were combined to give a 77:23 mixture (29 g) of the 2′ and 3′product. Pure 2′-O-nonyl product is obtained by chromatography. ¹H NMR(DMSO-d₆) δ 0.95 (t, 3, CH₃); 1.17 [m, 12, O—CH₂—CH₂—(CH₂)₆]; 1.42 [m,2, O—CH₂CH₂(CH₂)₆]; 3.27-3.70 (m, 2, H-5′); 3.50-3.70 [m, 2,O—CH₂(CH₂)₇]; 3.95 (m, 1, H-4′), 4.24 (m, 1, H-3′); 4.40 (m, 1, H-2′);5.10 (d, 1, 3′—OH, J=5 Hz); 5.50 (t, 1, 5′—OH, J=6 Hz); 5.76 (s, 2,2—NH₂); 5.83 (d, 1, H-1′, J=6.0 Hz); 6.81 (s, 2, 6—NH₂); and 7.96 (s, 1,8-H).

Example 13 2′-O-Nonylguanosine

A mixture of 2,6-diamino-9-(2′-O-nonyl-β-D-ribofuranosyl)purine and2,6-diamino-9-(3′-O-nonyl-β-D-ribofuranosyl)purine (≈80:20 mixture, 29g) in 0.1 M sodium phosphate buffer (50 ml, pH 7.4), 0.1 M tris buffer(1800 ml, pH 7.4) and DMSO (1080 ml) was treated with adenosinedeaminase (1.6 g) as per the procedure of Example 3 to yield 60 g ofproduct as an oil. An analytical product was purified by silica gelchromatography and recrystallized from EtOAc. m.p. 258-259° C. ¹H NMR(DMSO-d₆) δ 0.96 (t, 3, CH₃, J=7 Hz); 1.17 [m, 12, O—CH₂—CH₂—(CH₂)₆];1.42 [m, 2, O—CH₂CH₂(CH₂)₆]; 3.27-3.61 (m, 4, H-5′, O—CH₂(CH₂)₇]; 3.95(m, 1, H-4′), 4.10-4.13 (m, 2, H-2′, H-3′); 5.13-6.06 (m, 2, 3′—OH5′—OH); 5.80 (d, 1, H-1′, J=6.4 Hz); 6.47 (s, 2, 2—NH₂); 7.98 (s, 1,8-H) and 10.64 (s, 1, N₁ amide). Anal. Calcd. for C₁₉H₃₁N₅O₅: C, 55.73;H, 7.63; N, 17.10. Found: C, 55.67; H, 7.66; N, 17.02.

Example 14 N2-Isobutyryl-2′-O-nonylguanosine

2′-O-nonylguanosine (14.7 g) in pyridine (360 ml) was treated withtrimethylsilyl chloride (23.4 ml) and isobutyryl chloride (30.6 ml) asper the procedure of Example 4 to yield crude product (37 g). The crudematerial was purified by silica gel chromatography (eluted with 90/10CHCl₃/MeOH) to field 14.6 g of product re-crystallized from EtOAc. m.p.168-169° C. ¹H NMR (DMSO-d₆) δ 0.85 [t, 3, CH₃(nonyl)], 1.14 [m, 18,O—CH₂CH₂(CH₂)₆CH(CH₃)₂], 1.40 [m, 2, O—CH₂CH₂(CH₂)₆], 2.79 [m, 1,CH(CH₃)₂], 3.31-3.63 (m, 4, H-5′, O—CH₂(CH₂)₇]; 3.96 (m, 1, H-4′),4.27-4.37 (m, 2, H-2′, H-3′); 5.10 (t, 1, 5′—OH, J=5 Hz), 5.18 (d, 1,3′—OH, J=4 Hz), 5.91 (d, 1, H-1′, J=6.6 Hz), 8.31 (s, 1, 8-H), 11.73 (s,1, C₂ amide) and 12.11 (s, 1, N₁ amide). Anal. Calcd. for C₂₃H₃₇N₅O₆: C,57.60; H, 7.78; N, 14.60. Found: C, 57.63; H, 7.92; N, 14.62.

Example 15 N2-Isobutyryl-5′-dimethoxytrityl-2′-O-nonylguanosine

N2-Isobutyryl-2′-O-nonylguanosine (14.6 g, 30.4 mmol) was treated withdimethoxytrityl chloride (12.1 g, 34 mmol) in pyridine (200 ml) as perthe procedure of Example 5 to yield 16 g of purple foam prior tochromatography and 11.5 g after chromatography purification. ¹H NMR(DMSO-d₆) δ 0.84 [t, 3, CH₃(nonyl), J=7 Hz], 1.16 [m, 18,O—CH₂CH₂(CH₂)₆, CH(CH₃)₂], 1.43 [m, 2, O—CH₂CH₂(CH₂)₆], 2.77 [m, 1,CH(CH₃)₂], 3.18-3.63 (m, 4, H-5′, O—CH₂(CH₂)₇]; 3.74 (s, 6, DMTr O—CH₃)4.06 (m, 1, H-4′), 4.27 (m, 1, H-3′); 4.42 (m, 1, H-2′); 5.19 (d, 1,3′—OH, J=5 Hz), 5.94 (d, 1, H-1′, J=5.7 Hz), 6.83-7.38 (m, 13, DMTraromatic), 8.14 (s, 1, 8-H), 11.65 (s, 1, C₂ amide) and 12.11 (s, 1, N₁amide). Anal. Calcd. for C₄₄H₅₅N₅O₈: C, 67.59; H, 7.27; N, 8.96. Found:C, 67.59; H, 7.11; N, 8.80.

Example 16 N2-Isobutyryl-5′-dimethoxytrityl-2′-O-nonylguanosine3′-β-cyanoethyl-N,N-diisopropylphosphoramidite

N2-Isobutyryl-5′-dimethoxytrityl-2′-O-nonylguanosine (2.1 g) was treatedwith bis-(N,N-diisopropylamino)-2-cyanoethyl-phosphite (1.5 g) andN,N-diisopropylammonium tetrazolide (0.2 g) as per the procedure ofExample 6 to yield the product (2.0 g). ³¹P NMR (CDCl₃) δ 150.7 and150.4 (diastereomers).

Example 17 2,6-Diamino-9-(2,′3′-di-O-propyl-β-D-ribafuranosyl]purine

The procedure of Example 2 was repeated utilizing2,6-diamino-9-(β-D-ribofuranosyl)purine (10 g), NaH (3 g) and1-bromopropanl (10 ml) in DMF. After evaporation of the reactionsolvent, the reaction products were purified by silica gelchromatography. The slower moving component yielded 4.3 g of the2′-O-propyl product as a foam. This foam was crystallized from water toyield 3.6 g of product. The faster moving component isolated as an oilformed crystals upon standing. EtOH was added to the crystals, they werefiltered and wash 1× EtOH to yield 1.1 grams of 2′,3′-di-O-propylproduct. m.p. 165-167° C. ¹H NMR (DMSO-d₆) δ 0.80 and 0.92 (t, 6, CH₃),1.6 and 1.45 (m, 4, CH₂), 3.7-3.45 (br m, 6), 4.07 (m, 2), 4.5 (dd, 1),5.55 (br t, 1, 5′—OH), 5.8 (br s, 2, 6—NH₂), 5.85 (d, 1, H-1′), 6.84 (brs, 2, 2—NH₂) and 8.0 (s, 1, H-8). Anal. Calcd. for C₁₆H₂₆N₆O₄: C, 52.45;H, 7.15; N, 22.94. Found: C, 52.18; H, 7.19; N, 22.75.

Example 18N2,N6-Diisobutyryl-2,6-diamino-9-(2′-O-propyl-β-D-ribofuranosyl)purine

2,6-diamino-9-(2′-O-propyl-β-D-ribofuranosyl) purine (2.0 g) in pyridine(35 ml) was treated with trimethylsilyl chloride (3.9 ml, 5 eq) andisobutyryl chloride (3.2 ml, 5 eq) as per the procedure of Example 4 toyield a foam after silica gel chromatography. The foam was crystallizedfrom EtOAc/Hex to yield 2.2 g of product. m.p. 140-142° C. ¹H NMR(DMSO-d₆) δ 0.77 (t, 3, CH₃), 1.07, 1.16 [d, 12, 2 x CH(CH₃)₂], 1.5 (m,2, CH₂), 2.9, 3.03 [m, 2, 2 x CH(CH₃)₂], 3.4 (m, 1, H-5″), 3.58 (m, 3,OCH₂, H-5′), 3.95 (m, 1, H-4′), 4.3 (m, 1), 4.5 (m, 1), 5.02 (t, 1,5′—OH), 5.2 (d, 1, 3′—OH), 6.03 (d, 1, H-1′), 8.58 (s, 1, H-8), 10.39(br s, 1, NH), and 10.57 (br s, 1, NH).

Example 19N2,N6-Diisobutyryl-2,6-diamino-9-(5′-O-dimethoxytrityl-2′-O-propyl-β-D-ribafuranosyl)purine

N2,N6-Diisobutyryl-2,6-diamino-9-(2′-O-propyl-β-D-ribo-furanosyl)purine(1.9 g) was treated with dimethoxytrityl chloride (1.5 g, 1.1 eq), anddimethylaminopyridine (20 mg as a catalyst) in pyridine (50 ml) as perthe procedure of Example 5 to yield the product as a foam (2.8 g). ¹HNMR (DMSO-d₆) δ 0.79 (t, 3, CH₃), 1.07, 1.16 [d, 12, 2 x CH(CH₃)₂], 1.5(m, 2, CH₂), 2.9, 3.03 [m, 2, 2 x CH(CH₃)₂], 3.58 (m, 3, OCH₂, H-5′),4.15 (m, 1, H-4′), 4.4 (m, 1), 4.6 (m, 1), 5.15 (d, 1, 3′—OH), 6.15 (d,1, H-1′), 6.8-7.35 (m, 13, DMTr), 8.5 (s, 1, H-8), 10.3 (br s, 1, NH),and 10.57 (br s, 1, NH).

Example 20 N2,N6-Diisobutyryl-2,6-diamino-9-(5′-O-dimethoxytrityl-2′-O-propyl-β-D-ribofuranosyl) purine3′-β-cyanoethyl-N,N-diisopropylphosphoramidite

N2,N6-Diisobutyryl-2,6-diamino-9-(5′-O-dimethoxytrityl-2′-O-propyl-β-D-ribofuranosyl) purine (2.6 g) wastreated with bis-(N,N-diisopropylamino)-2-cyanoethylphosphite (1.7 g)and N,N-diisopropylammonium tetrazolide (300 mg) overnight at roomtemperature. The reaction mixture was partitioned against dil.Na₂CO₃/CHCl₂ and then Na₂CO₃/NaCl and dried over MgSO₄. The organiclayer was evaporated to a foam. The foam was dissolved in CH₂C12 (≈8 ml)and slowly added to Hexanes (500 ml). The solid was filtered and driedto yield the product as a powder (3.1 g). ³¹P NMR (CDCl₃) δ 150.8 and151.3.

Example 212,6-Diamino-9-[2′-O-[(N-phthalimido)prop-3-yl]-β-D-ribofuranosyl]purinea2,6-Diamino-9-[3′-O-[(N-phthalimido)prop-3-yl]-β-D-ribo-furanosyl]purine

2,6-Diamino-9-(β-D-ribofuranosyl)purine (14.2 g) was treated with sodiumhydride (3 g, 1.5 eq) and N-(3-bromopropyl) phthalimide (5.3 ml, 1.5 eq)in DMF (20 g) at 70° C. overnight. The reaction mixture was proportionedbetween H₂O and Hexanes (1×) and the aqueous layer then extracted4×CH₂Cl₂. The organic layer was dried over MgSO₄ and evaporated to aresidue. The residue was purified by silica gel chromatography elutedwith MeOH/CH₂Cl₂. The 2′-O-(N-phthalimido)propyl product eluted firstfollowed by mixed fractions and then the 3′-O-(N-phthalimido) product.Evaporations of the fractions gave 3.4 q of the2′-O-(N-phthalimido)propyl product, 3.0 g of mixed 2′and 3′ products and1.4 g of the 3′-O-(N-phthalimido)propyl product all as foams. The3′-O-(N-phthalimido)propyl product was crystallized from EtOAc/MeOH togive 270 mg of solid.

2,6-Diamino-9-[2′-O-[(N-phthalimido)prop-3-yl]-β-D-ribofuranosyl] purine

¹H NMR (DMSO-d₆) δ 1.8 (tq, 2, —CH₂—), 3.4-3.58 (m, 6, 2x CH₂, H-5′),3.9 (m, 1), 4.26 (m, 1), 4.37 (m, 1), 5.05 (br d, 1, 3′—OH), 5.4 (br t,1, 5′—OH), 5.72 (br s, 2, NH₂), 5.8 (br d, 1, H-1′), 6.75 (br s, 2,NH₂), 7.8 (br 8, 4, Ar) and 8.93 (s, 1, H-8).

2,6-Diamino-9-[3′-O-[(N-phthalimido)prop-3-yl]-β-D-ribofuranosyl] purine

m.p. 220-222° C., ¹H NMR (DMSO-d₆) δ 1.85 (tq, 2, —CH—N), 3.6-3.67 (m,4, —O—CH₂, H-5′), 3.85 (m, 1), 3.92 (m, 1), 4.6 (m, 1), 5.33 (d, 1,2′—OH), 5.45 (br t, 1, 5′—OH), 5.65 (d, 1, H-1′), 5.73 (br s, 2, NH₂),6.75 (br d, 2, NH₂), 7.8-7.85 (m, 4, Ar) and 7.85 (s, 1, H-8). Anal.Calcd. for C₂₁H₂₃N₇O₆: C, 53.73; H, 4.94; N, 20.88. Found: C, 53.59; H,4.89; N, 20.63.

Example 22 2′-O-[(N-Phthalimido)prop-3-yl] guanosine

2,6-diamino-9-[2′-O-[(N-phthalimido)prop-3-yl]-β-D-ribofuranosyl] purine(3.1 g) in 0.1 M sodium phosphate buffer (3 ml, pH 7.4), 0.05 M trisbuffer (65 ml, pH 7.4) and DMSO (45 ml) was treated with adenosinedeaminase (200 mg) at room temperature for 5 days as per the procedureof Example 3. The product containing fractions from the silica gelchromatography were evaporated and upon concentration formed whitecrystals. The crystals were filtered and washed with MeOH to yield 1.1 gof product. An analytical sample was recrystallized from MeOH. m.p.192-194° C. ¹H NMR (DMSO-d₆) δ 1.82 (m, 2, CH₂), 3.45-3.67 (m, 6, H-5′,OCH₂, NCH₂), 3.9 (m, 1), 4.3 (m, 2, H-2′, H-3′), 5.1 (m, 2, 5′ and3′—OH), 5.8 (d, 1, H-1′), 6.5 (br s, 2, NH₂), 7.83 (s, 4, phthal), 7.98(s, 1, H-8) and 10.5 (br s, 1, NH). Anal. Calcd. for C₂₁H₂₂N₆O₇.½H₂O: C,52.61; H, 4.83; N, 17.53. Found: C, 52.52; H, 4.78; N, 17.38.

Example 23 N2-Isobutyryl-2′-O-[(N-phthalimido)prop-3-yl] quanosine

2′-O-[(N-phthalimido)prop-3-yl] guanosine (7.2 g, crude) in pyridine (35ml) was treated with trimethylsilyl chloride (11.6 ml, 5 eq) andisobutyryl chloride (8 ml, 5 eq) as per the procedure of Example 4 toyield the product as a crude foam (6.5 g). An analytical sample wasobtained by crystallization from EtOAc. m.p. 166-168° C. ¹H NMR(DMSO-d₆) δ 1.15 [d, 6, —CH(CH₃)₂], 1.85 (m, 2, CH₂), 2.8 [m, 1,CH(CH₃)₂], 3.45-3.7 (m, 6, H-5′, OH₂, NCH₂), 3.95 (m, 1), 4.34 (m, 1),4.4 (m, 1), 5.12 (t, 1, 5′—OH), 5.18 (d, 1, 3′—OH), 5.93 (d, 1, H-1′),7.83 (s, 4, phthal), 8.3 (s, 1, H-8), 11.65 (br 5, 1, NH) and 12.1 (brs, 1, NH). Anal. Calcd. for C₂₅H₂₈N₆O₈.½H₂O: C, 54.64; H, 5.32; N.15.29. Found: C, 54.46; H, 5.39; N, 14.98.

Example 24N2-Isobutyryl-5′-dimethoxytrityl-2′-O-[(N-phthalimido)prop-3-yl]quanosine

N2-Isobutyryl-2′-O-[(N-phthalimido)prop-3-yl] guanosine (1.2 g) wastreated with dimethoxytrityl chloride (820 mg, 1.1 eq), anddimethylaminopyridine (20 mg as catalyst) in pyridine (50 ml) as per theprocedure of Example 5 utilizing 1:1 Hex/EtOAc, then EtOAc then 5%MeOH/EtOAc with 1%t TEA as eluent. The product containing fraction wereevaporated to yield the product as a foam (1.7 g). ¹H NHR (DMSO-d₆) δ1.1 [d, 6, —CH(CH₃)₂], 1.85 (m, 2, CH₂), 2.75 [m, 1, CH(CH₃)₂], 3.45-3.7(m, 6, H-5′, OCH₂, NCH₂), 3.75 (s, 6, OCH₃), 4.0 (m, 1), 4.32 (m, 1),4.4 (m, 1), 5.2 (d, 1, 3′—OH), 5.93 (d, 1, H-1′), 6.83, 7.2, 7.35 (m,13, DMTr), 7.78 (m, 4, phthal), 8.15 (s, 1, H-8), 11.6 (br s, 1, NH) and12.05 (br s, 1, NH). Anal. Calcd. for C₄₆H₄₆N₆O₁₀.H₂O: C, 64.18; H,5.62; N, 9.76. Found: C, 64.42; H, 5.78; N, 9.53.

Example 25N2-Isobutyryl-5′-dimethoxytrityl-2′-O-[(N-phthalimido)prop-3′-yl]guanosine3′-β-cyanoethyl-N,N-diisopropylphosphoramidite

N2-Isobutyryl-5′ -dimethoxytrityl-2′-O-[(N-phthalimide) prop-3-yl]guanosine (1.6 g) was treated withbis-(N,N-diisopropylamino)-2-cyanoethylphosphite (1.48 g) andN,N-diisopropylamonium tetrazolide (200 mg) as per the procedure ofExample 6 to yield the product (2.0 g) ³¹P NMR (CDCl₃) δ150.9.

Example 26N2-Dimethylminomethylidene-5′-dimethoxytrityl-2′[(N-phthalimido)prop-3-yl]quanosine

2′-O-[(N-phthalimido)prop-3-yl]guanosine (900 mg) in DMF (20 ml) wastreated with N,N-dimethylformamide dimethyl acetal (2 ml). The reactionmixture was stirred for 2 hr and evaporated under high vac at 52° C. Theresidue was co-evaporated 1× with pyridine and taken up in solution inpyridine. Dimethoxytrityl chloride (713 mg, 1.1 eq) anddimethylaminopyridine (20 mg as a catalyst) were added. This reactionmixture was stirred overnight, partitioned between Na₂CO₃/CH₂Cl₂, driedover MgSO₄ and purified by silica gel chromatography as per theprocedure of Example 5 to yield 1.7 g of product as an off white solid.¹H NMR (DMSO-d₆) δ 1.88 (m, 2, CH₂), 3.1 [d, 6, N═CHN(CH₃)₂], 3.3 (m, 2,H-5′), 3.67 (m, 4, OCH₂, NC₂), 3.78 (s, 6, 2x OCH₃), 4.0 (m, 1, H-4′),4.35 (m, 2, H-2′, H-3′), 5.2 (d, 1, 3′—OH), 5.95 (d, 1, H-1′), 6.85,7.25, 7.39 (m, 13, DMTr), 7.85 (s, 4, phthal), 7.95 [s, 1, H-8), 8.5 (s,1, N═CHN(CH₃)_(2]) and 11.39 (s, 1, NH₂). Anal. Calcd. forC₄₅H₄₅N₇O₉.½H₂O: C, 64.58; H, 5.54; N, 11.71. Found: C, 64.10; H, 5.65;N, 11.47.

Example 27N2-Dimethylminomethylidene-5′-dimethoxytrityl-2′-O-[(N-phthalimido)prop-3-yl]guanosine 3′-β-cyanoethyl-N,N-diisopropylphosphoramidite

N2-dimethylaminomethylidene-5′-dimethoxytrityl-2′-O-[(N-phthalimido)prop-3-yl]guanosine (1.7 g), bis-(N,N-diisopropylamino)-2-cyanoethylphosphite (1.4ml) and N,N-diisopropylammonium tetrazolide (170 mg) were stirredovernight: at room temperature. The reaction mixture was partitionedbetween CH₂Cl₂ and Na₂CO₃ (2×). The organic phase was dried over MgSO₄and evaporated to an oil. The oil was dissolved in a minimum of CH₂Cl₂and added dropwise to ≈900 ml Hexanes to precipitate the product. Thesolid was isolated and dried to yield 2.1 g of product. ¹P NMR (CDCl₃) δ150.4, 150.6.

Example 282,6-Diamino-9-[2′-O-(N-phthalimido)pent-5-yl]-β-D-ribofuranosyl] purine

2,6-Diamino-(9-β-D-ribofuranosyl)purine (6.7 g) was treated with sodiumhydride (1.3 g) and N-(5-bromopentyl) phthalimide (7.8 g, 1.1 eq) in DMF(60 ml) at room temperature for three days. The reaction mixture wasproportioned between H₂O and CH₂Cl₂ and extracted 4x CH₂Cl₂. Thecombined organic layers were dried over MGSO₄ and evaporated. Theresidue was purified by silica gel chromatography eluted with 5→10%MeOH/CH₂Cl₂. The 2′-O-(N-phthalimido)pentyl containing fractions werecollected and evaporated to a yellow foam to give 2.2 g of product. Ananalytical sample was crystallized from EtOH. m.p. 173-175° C. ¹H NMR(DMSO-d₆) δ 1.2 (m, 2, —CH₂—), 1.47 (m, 4, 2x CH₂), 3.55, 3.65 (m, 6,O—CH₂, H-5′, NCH₂), 3.95 (m, 1), 4.28 (m, 1), 4.4 (m, 1), 5.13 (d, 1,3′—OH), 5.5 (t, 1, 5′—OH), 5.77 (br s, 2,6—NH₂), 5.84 (br d, 1, H-1′),6.8 (br s, 2, 2—NH₂), 7.86 (M, 4, phthal) and 7.95 (s, 1, H-8). Anal.Calcd. for C₂₃H₂₇N₇O₆: C, 55.50; H, 5.47; N, 19.71. Found: C, 55.44; H,5.51; N, 19.30.

Example 29 2′-O-[(N-Phthalieido)pent-5-yl] guanosine

A mixture of the 2,6-diamino-9-[2′-O-[(N-phthalimido)pent-5-yl]-β-D-ribofuranosyl]purine and2,6-diamino-9-[3′-O-[(N-phthalimido) pent-5-yl]-β-D-ribofuranosyl]purineisomers (2.2 g) in 0.1 M tris buffer (60 ml, pH 7.4), 0.1 M NaPO₄ buffer(2 ml, pH 7.4) and DMSO (40 ml) was treated with adenosine deaminase (60mg) at room temperature for 5 days as per the procedure of Example 3.The product containing fractions from the silica gel chromatography wereevaporated to give the product (1.0 g) as a crude white solid. Ananalytical sample was prepared by the addition of MeOH to formcrystals;. m.p. 178-180° C. ¹H NMR (DMSO-d₆) δ 1.24 (m, 2, CH₂), 1.5 (m,4, 2x C₂), 3.5-3.6 (m, 6, H-5′, OCH₂, NCH₂), 3.87 (m, 1, H-4′), 4.25 (m,2, H-2′, H-3′), 5.1 (m, 2, 5′ and 3′—OH), 5.78 (d, 1, H-1′), 6.5 (br s,2, NH₂), 7.84 (M, 4, phthal), 7.98 (s, 1, H-8) and 10.67 (br s, 1, NH).Anal. Calcd. for C₂₃H₂₆N₆O₇.½H₂O: C, 54.43; H, 5.36; N, 16.56. Found: C,54.79; H, 5.24; N, 16.61.

Example 30 N2-Isobutyryl-2′-O-[(N-phthalimido)pent-5-yl] quanosine

2′-O-[(N-phthalimido)pent-5-yl] guanosine (1.6 g, crude) in pyridine (35ml) was treated with trimethylsilyl chloride (2.0 ml, 5 eq) andisobutyryl chloride (1.68 ml, 5 eq) as per the procedure of Example 4 toyield the product as a foam. This foam was co-evaporated 2× with EtOAcfollowed by the addition of EtOAc and heating to yield white crystals(950 mg). m.p. 202-204° C. ¹H NMR (DMSO-d₆) δ 1.1 [d, 6, CH(CH₃)₂], 1.17(m, 2, CH₂), 1.43 (m, 4, 2x CH₂), 2.74 [m, 1, CH(CH₃)₂], 3.45-3.55 (m,6, H-5′, OCH₂, NCH₂), 3.9 (m, 1), 4.23 (m, 1), 4.3 (m, 1), 5.07 (t, 1,5′—OH), 5.15 (d, 1, 3′—OH), 5.87 (d, 1, H-1′), 7.8 (s, 4, phthal), 8.27(s, 1, H-8), 11.67 (br s, 1, NH) and 12.06 (br s, 1, NH). Anal. Calcd.for C₂₇H₃₂N₆O₈.½H₂O: C, 56.14; H, 5.76; N, 14.55. Found: C, 56.45; H,5.74; N, 14.41.

Example 31N2-Isobutyryl-5′-dimethoxytrityl-2′-O-[(N-phthalimido)pent-5-yl]quanosine

N2-Isobutyryl-2′-O-[(N-phthalimido)pent-5-yl] guanosine (0.95 g) wastreated with dimethoxytrityl chloride (620 mg, 1.1 eq), anddimethylaminopyridine (20 mg as a catalyst) in pyridine (50 ml) as perthe procedure of Example 5 utilizing EtOAc 1% TEA and then 5% MeOHEtOAc/CH₂Cl₂ with 1% TEA as eluent. The product containing fractionswere evaporated to yield the product as a foam (1.4 g). ¹H NMR (DMSO-d₆)δ 1.14 [d, 6, —CH(CH₃)₂], 1.25 (m, 2, CH₂), 1.53 (m, 4, 2x CH₂), 2.77[m, 1, CH(CH₃)₂], 3.3-3.6 (m, 6, H-5′, OCH₂, NCH₂), 3.75 (s, 6, OCH₃),4.07 (m, 1), 4.33 (m, 1), 4.4 (m, 1), 5.18 (d, 1, 3′—OH), 5.94 (d, 1,H-1′), 6.83, 7.2, 7.53 (m, 13, DMTr), 7.8 (s, 4, phthal), 8.15 (s, 1,H-8), 11.6 (br s, 1, NH) and 12.1 (br s, 1, NH). Anal. Calcd. forC₄₈H₅₀N₆O₁₀.½H₂O: C, 65.52; H, 5.84; N, 9.55. Found: C, 65.55; H, 5.94;N, 9.20.

Example 322,6-Diamino-9-[3′,5′-O-(taetraisopropyldisiloxane-1,3-diyl)-β-D-ribofuranosyl]purine

To a suspension of 2,6-diamino-9-(β-D-ribofuranosyl)purine (10.5 g) inpyridine (100 ml) was added 1,3-dichlorotetraisopropyldisiloxane (TIPDS,12.6 g). The reaction was stirred at room temperature for 4 hours and anadditional. 1.3 g of 1,3-dichlorotetraisopropyldisiloxane was addedfollowed by stirring overnight. The reaction mixture was poured into icewater and the insoluble product (11.6 g) collected by filtration. Ananalytical sample was recrystallized from EtOAc/Hexanes. m.p. 170-172°C. Anal. Calcd. for C₂₂H₄₀N₆O₅Si₂.½H₂O: C, 49.5; H, 7.74; N, 15.7.Found: 49.57; H, 7.82; N, 15.59.

Example 332,6-Diamino-9-[3′,5′-O-(tetraisopropyldisiloxane-1,3-diyl)-2-O-methyl-β-D-ribofuranosyl]purine

A mixture of2,6-Diamino-9-[3,5-O-(tetraisopropyldisiloxane-1,3-diyl)-β-D-ribofuranosyl]purine(8.8 g) in DMF (120 ml) and methyl iodide (3 ml, 3 eq) was cooled in anice bath and NaH (60% in oil, 1.0 g, 1.5 eq) added. After 20 min thereaction was quenched with MeOH and partitioned between sat. NH₄Cl andCH₂Cl₂. The organic phase was washed with 1x NH₄Cl, dried over MgSO₄ andevaporated. The residue was crystallized from hot EtOH/H₂O to yield theproduct (8.5 g) as crystals. m.p. 87-89° C. ¹H NMR (DMSO-d₆) 1.05 (m,28, TIPDS), 3.57 (s, 3, OCH₃), 3.98 (m, 1, H-4′), 3.92 and 4.07 (ABX, 2,H-5′), 4.13 (d, 1), 4.6 (dd, 1, H-3′), 5.76 (br s, 2, NH₂), 5.8 (s, 1,H-1′), 6.77 (br s, 2, NH₂) AND 7.77 (s, 1 H-8).

Example 34 2,6-Diamino-9-(2′-O-methyl-β-D-ribofuranosyl)purine

To a solution of2,6-Diamino-9-[3′,5′-O-(tetraisopropyldisiloxane-1,3-diyl)-2′-O-methyl-β-D-ribofuranosyl]purine(8.5 g) in THF (50 ml) was added 1M tetrabutylammonium fluoride in THF(Aldrich, 20 ml). The reaction mixture was stirred for 2 hrs andfiltered. The filter cake was washed with 2× EtOAc and air dried to give4.0 g of crude product. An analytical sample was crystallized from hotNeOH. m.p. 133-135° C. ¹H NMR (DMSO-d₆) δ 3.3 (s, 3, OCH₃), 3.58 (m, 2,H-5′), 3.98 (m, 1, H-4′), 4.28 (m, 2, H-2′, H-3′), 5.23 (br s, 1,3′—OH), 5.48 (br t, 1, 5′—OH), 5.77 (br s, 2, NH₂), 5.82 (d, 1, H-1′),6.83 (br s, 2, NH₂) and 7.95 (s, 1, H-8). Anal. Calcd. forC₁₁H₁₆N₆O₄.½H₂O: C, 43.28; H, 5.61; N, 27.52. Found: C, 43.51; H. 5.62;N, 27.26.

Example 35 2′-O-Methylguanosine

2,6-Diamino-9-(2′-O-methyl-β-D-ribofuranosyl) purine (9.5 g) in 0.1Msodium phosphate buffer (200 ml, pH 7.4) and DMSO (25 ml) was treatedwith adenosine deaminase (Type II Sigma) at RT for 4 days. The resultingsuspension was cooled and filtered and the resulting filter cake washedwith H₂O and dried to a white solid (4.0 g). The solid wasrecrystallized from hot H₂O to yield 2.9 g of product. m.p. 236-238° C.¹H NMR (DMSO-d₆) δ 3.3 (s, 3, OCH₃), 3.53 and 3.6 (ABX, 2, H-5′), 3.87(m, 1, H-4′), 4.15 (m, 1, H-2′), 4.25 (m, 1, H-3′), 5.13 (t, 1, 5′—OH),5.23 (d, 1, 3′—OH), 5.8 (d, 1, H-1′), 6.48 (br s, 2, NH₂), 7.96 (s, 1,H-8) and 10.68 (br s, 1, NH). Anal. Calcd. for C₁₁H₁₅N₅O₅.½H₂O: C,43.14; H, 5.26; N, 22.86. Found: C, 43.59; H, 5.34; N. 23.04.

Example 36 N2-Isobutyryl-2′-O-methylquanosine

2′-O-methylguanosine (3.5 g) in pyridine (100 ml) was treated withtrimethylsilyl chloride (9 ml, 6 eq) and isobutyryl chloride (6.2 ml) atRT for 4 hr. The reaction mixture was cooled in an ice bath, H₂O (20 ml)was added and stirring continued for an additional 20 min. NH₄OH (20 ml)was added and after stirring for 30 min the reaction mixture waitevaporated. The residue was triturated with H₂O, filtered and thefiltrate evaporated and purified by silica gel chromatography as per theprocedure of Example 4 to yield the product as an off white solid (1.5g). ¹H NMR (DMSO-d₆) δ 1.1 [d, 6, CH(CH₃)₂], 2.77 [m, 1, CH(CH₃)₂],3.33-3.6 (m, 5, OCH₃, H-5′), 3.93 (m, 1, H-4′), 4.22 (m, 1), 4.3 (m, 1),5.1 (t, 1, 5′—OH), 5.28 (d, 1, 3′—OH), 5.9 (d, 1, H-1′), 8.28 (s, 1,H-8) and. 11.9 (br s, 1, NH).

Example 37 N2-Isobutyryl-5′-dimethoxytrityl-2′-O-methylguanosine

N2-Isobutyryl-2′-O-methylguanosine (1.5 g) was treated withdimethoxytrityl chloride (1.5 g, 1.1 eq), and dimethylaminopyridine (100mg as a catalyst) in pyridine (50 ml) as per the procedure of Example 5to yield the product as a foam (2.6 g). ¹H NMR (DMSO-d₆) δ 1.14 (d, 6,CH(CH₃)₂], 2.75 [m 1, CH(CH₃)₂], 3.5 (m, 2, H-5′), 3.74 (s, 6, OCH₃),4.05 (m, 1), 4.33 (m, 1), 5.26 (d, 1, 3′—OH), 5.95 (d, 1, H-1′), 6.83,7.2, 7.35 (m, 13, DMTr), 8.15 (s, 1, H-8), 11.6 (br s, 1, NH) and 12.1(br s, 1, NH).

Example 38 N2-Isobutyryl-5′-dimethoxytrityl-2′-O-methylguanosine3′-β-cyanoethyl-N,N-diisopropylphosphoramidite

N2-Isobutyryl-5′ -dimethoxytrityl-2′-O-methylguanosine (20 g) wastreated with bis-(N,N-diisopropylamino)-2′-cyanoethylphosphite (10.8 g)and N,N-diisopropylammonium tetrazolide (1.6 g) as per the procedure ofExample 6 to yield the product (15.7 g). ³¹P.NMR (CDCl₃) δ 148.97 and147.96.

Example 39N2,N6-Diisobutyryl-2,6-diamino-9-(2′-O-methyl-β-D-ribofuranosyl) purine

2,6-diamino-9-(2′-O-methyl-β-D-ribofuranosyl) purine (700 mg) inpyridine (20 ml) was treated with trimethylsilyl chloride (2.1 ml, 7 eq)and isobutyryl chloride (1.25 ml, 5 eq) as per the procedure of Example4 to yield the product as a foam (900 mg) after silica gelchromatography.

Example 40N2,N6-Diisobutyryl-2,6-diamino-9-(5′-O-dimethoxytrityl-2′-methyl-β-D-ribofuranosyl)purine

N2,N6-Diisobutyryl-2,6-diamino-9-(2′-O-methyl-β-D-ribofuranosyl)purine(900 mg) was treated with dimethoxytrityl chloride (1.0 g) anddimethylaminopyridine (20 mg as a catalyst) in pyridine (30 m) as perthe procedure of Example 5 to yield the product as a foam (700 mg). ¹HNMR (DMSO-d₆) δ0.96-1.16 [m, 12, 2x CH(CH₃)₂], 2.9 and 3.05 [M, 2, 2xCH(CH₃)₂], 3.18 and 3.37 (ABX, 2, H-5′), 3.38 (s, 3, OCH₃), 3.7 (s, 6,OCH₃), 4.05 (m, 1, H-4′), 4.44 (m, 2, H-2′,H-3′), 5.24 (d, 1, 3′—OH),6.06 (d, 1, H-1′), 6.78, 7.2, 7.33 (m, 13, Ar), 8.22 (s, 1, H-8), 10.3(br s, 1, NH) and 10.57 (br s, 1, NH).

Example 41 N2,N6-Diisobutyryl-2,6-diamino-9-(5′-O-dimethoxytrityl-2′-O-methyl-β-D-ribofuranosyl)purine3′-β-cyanoethyl-N,N-diisopropylphosphoramidite

N2,N6-Diisobutyryl-2,6-diamino-9-(5′-O-dimethoxytrityl-2′-O-methyl-β-D-ribofuranosyl)purine (600 mg ) was treated withbis-(N,N-diisopropylamino)-2-cyanoethylphosphite (500 μl) andN,N-diisopropylammonium tetrazolide (80 mg) overnight at RT. Thereaction mixture was partitioned against dil. Na₂CO₃/CHCl₂ and thenNa₂CO₃/NaCl and dried over MgSO₄. The organic layer was evaporated to afoam (500 mg). ³¹ P NMR (CDCl₃) δ 151.1 (doublet).

Example 42 2,6-Diamino-9-(2′-O-octadecyl-β-D-ribofuranosyl) purine

2,6-Diamino-9-(β-D-ribofuranosyl)purine (50 g, 180 mmol) and sodiumhydride (7 g) in DMF (1 l) were heated to boiling for 2 hr.Iodooctadecane (100 g) was added at 150° C. and the reaction mixtureallowed to cool to RT. The reaction mixture was stirred for 11 days atRT. The solvent was evaporated and the residue purified by silica gel.chromatography. The product was eluted with 5% MeOH/CH₂Cl₂. The productcontaining fraction were evaporated to yield the product (11 g). ¹H NMR(DMSO-d₆) δ 0.84 (t, 3, CH₂); 1.22 [m, 32, O—CH₂—CH₂—(CH₂)₁₆—]; 1.86 (m,2, O—CH₂CH₂—); 3.25 (m, 2, OCH₂—); 3.93 (d, 1, 4′H), 4.25 (m, 1, 3′H);4.38 (t, 1, 2′H); 5.08 (d, 1, 3′—OH); 5.48 (t, 1, 5′—OH); 5.75 (s,2,6—NH₂); 5.84 (d, 1, 1′-H); 6.8 (s, 2, 2—NH₂); and 7.95 (s, 1, 8-H).

Example 43 2′-O-octadocylguanosine

2,6-Diamino-9-(2′-O-octadecyl-β-D-ribofuranosyl) purine (10 g) in 0.1 Msodium phosphate buffer (50 ml, pH 7.4) 0.1 M tris buffer (1000 ml, pH7.4) and DMSO (1000 ml) was treated with adenosine deaminase (1.5 g) asper the procedure of Example 3. At day 3, day 5 and day 7 an additionalaliquot: (500 mg, 880 mg and 200 mg, respectively) of adenosinedeaminase was added. The reaction was stirred for a total of 9 day andafter purification by silica gel chromatography yielded the product (2g). An analytical sample was recrystallized from MeOH ¹H NMR (DMSO-d₆) δ0.84 (t, 3, CH₃), 1.22 [s, 32, O—CH₂—CH₂—(CH₂)₁₆], 5.07 (m, 2, 3′—OH5′—OH); 5.78 (d, 1, 1′-H); 6.43 (s, 2, NH₂), 7.97 (s, 1, 8-H) and 10.64(s, 1, NH₂). Anal. Calcd. for C₂₈H₄₉N₅O₅: C, 62.80; H, 9.16; N, 12.95.Found: C, 62.54; H, 9.18; N, 12.95.

Example 44 N2-Isobutyryl-2′-O-oatadecylguanosine

2′-O-Octadecylguanosine (1.9 g) in pyridine (150 ml) was treated withtrimethylsilyl chloride (2 g, 5 eq) and isobutyryl chloride (2 g, 5 eq)as per the procedure of Example 4. The product was purified by silicagel chromatography (eluted with 3% NeOH/EtOAc) to yield 1.2 g ofproduct. ¹H NMR (DMSO-d₆) δ 0.85 [t, 3, CH₃], 1.15 [m, 38,O—CH₂CH₂(CH₂)₁₆, CH(Cl₃)₂], 2.77 [m, 1, CH(CH₃)₂], 4.25 (m, 2, 2′H,3′H); 5.08 (t, 1, 5′—OH), 5.12 (d, 1, 3′—OH), 5.87 (d, 1, 1′-H), 8.27(s, 1, 8-H), 11.68 (s, 1, NH₂) and 12.08 (s, 1, NH₂). Anal. Calcd. forC₃₂H₅₅N₅O₆: C, 63.47; H, 9.09; N, 11.57. Found: C, 63.53; H, 9.20; N,11.52.

Example 45 2,6-Diamino-9-[2′-O-(imidazol-1-yl)butyl-β-D-ribofuranoasyl]purine

2,6-Diamino-(9-β-D-ribofuranosyl) purine (5.0 g) in DMF (400 ml) wastreated with sodium hydride (0.78 g). After stirring an additional 30min a further portion of sodium hydride (2.6 g) was added immediatelyfollowed by bromobutyl-imidazole (9.9 g) in DMF (25 ml). The reactionmixture was stirred overnight and quenched with H₂O. The reactionmixture was filtered through celite and evaporated to yield an oilyproduct. TLC showed a mixture of isomers.

Example 46 2′-O-(Imidazol-1-yl)butylguanosine

A mixture of the2,6-diamino-9-[2′-O-(imidazol-1-yl)butyl-β-D-ribofuranosyl]purine and2,6-diamino-9-[3′-(imidazol-1-yl)butyl-β-D-ribofuranosyl]purine isomersin 0.1 M tris buffer (pH 7.4), 0.1 M NaSO₄ buffer (pH 7.4) and DMSO istreated with adenosine deaminase at RT for 5 days as per the procedureof Example 3. The product containing fractions are purified by silicagel chromatography and the product containing fraction evaporated togive the product.

Example 47 N2-Isobutyryl-2′-O-(imidazol-1-yl)butylguanosine

2′-O-(imidazol-1-yl)butylguanosine in pyridine will be treated withtrimethylsilyl chloride (5 eq) and isobutyryl chloride (5 eq) as per theprocedure of Example 4 to yield the product.

Example 48N2-Isobutyryl-5′-dimethoxytrityl-2′-O-(imidazol-1-yl)butylguanosine

N2-Isobutyryl-2′-O-(imidazol-1-yl)butylguanosine will be treated withdimethoxytrityl chloride (1.1 eq), and dimethylaminopyridine (as acatalyst) in pyridine as per the procedure of Example 5. Afterchromatography purification, the product containing fractions will beevaporated to yield the product).

Example 49 2′,3′-O-Dibutylstannylene uridine

Utilizing the protocol of Wagner, et al., J. Org. Chem. 1974, 39, 24,uridine (45 g, 0.184 mol) was refluxed with di-n-butyltinoxide (45 g,0.181 mol) in 1.4 l of anhydrous methanol for 4 hrs. The solvent wasfiltered and the resultant 2′,3′-O-dibutylstannylene-uridine was driedunder vacuum al: 100° C. for 4 hrs to yield 81 g (93%).

Example 50 2′-O-[Pentyl-ω-(N-phthalimido)]uridine

2′,3′-O-Dibutyl stannylene-uridine was dried over P₂O₅ under vacuum for12 hrs. To a solution of this compound (20 g, 42.1 mols) in 500 ml ofanhydrous DMF were added 25 g (84.2 mmols) ofN(5-bromopentyl)phthalimide (Trans World Chemicals, Rockville, Md.) and12.75 g (85 mmols) of cesium fluoride (CsF). The mixture was stirred atroom temperature for 72 hrs. The reaction mixture was evaporated thenco-evaporated once with toluene and the residue was partitioned betweenEtoAc and water (400 ml each). The EtOAc layer was concentrated andapplied to a silica column (700 g). Elution with CH₂Cl₂—CH₃OH (20:1,v/v) gave fractions containing a mixture of the 2′- and 3′- isomers ofO-pentyl-ω-N-phthalimido uridine, in 50% yield.

Example 51 5′-O-Dimethoxytrityl-2′-O-[pentyl-ω-(N-phthalimido)]uridine

The isomeric mixture of 2′-O-[pentyl-ω-(N-phthalimido)]uridine wasallowed to react with DMT chloride in dry pyridine at room temperaturefor 6 hrs. CH₃OH was used to quench excess DMT-Cl and the residue waspartitioned between CH₂Cl₂ containing 0.5% Et₃N and water. The organiclayer was dried (MgSO₄) and the residue was applied to a silica column.The column was eluted with CH₂Cl₂:CH₃OH (20:1, v/v) to separate the 2′and 3′ isomers of the product.

Example 52 5′-O-Dimethoxytrityl-2′-O-[pentyl-ω-(N-phthalimido)]uridine-3′-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

5′-O-Dimethoxytrityl-2′-O-[pentyl-ω-(N-phthalimido)]uridine was placedin a dry round bottom flask containing a teflon stir-bar. The flask waspurged with argon. Anhydrous methylene chloride was added to the flaskin an amount sufficient to dissolve the nucleoside. Previously vacuumdried N,N-diisopropylaminohydrotetrazolide (600 mq, 0.014 mol) was addedunder argon. Bis-N,N-diisopropylamino-cyanoethylphosphite was added viasyringe. The reaction was stirred under argon at 25° C. for 16 h. Uponcompletion of the reaction, the reaction was transferred to a separatoryfunnel. The reaction flask was rinsed with methylene chloride (2×50 mL).The combined organic layer was washed 2× with sat'd aq. sodiumbicarbonate. The organic layer was dried over magnesium sulfate,evaporated and taken up in toluene containing 1% triethylamine. Theresulting phosphoramidite was purified by silica gel flashchromatography and eluted with 3:1→1:1 Hexanes/ethyl acetate containing1% triethylamine. Selected fractions were combined, concentrated underreduced pressure and dried to yield the product as a white foam. ³¹P-NMR(CDCl₃, H₃PO₄ std.) showed the correct diastereomers

Example 53 2′-O-Pentyluridine

Utilizing the procedures of Examples 50 and 51,2′,3′-O-dibutylstannylene uridine (19.1 g) was treated with bromopentane(7 ml, 1.3 eq.) and sodium iodide (4.5 g) in DMF (90 ml). Purificationon a silica gel column utilizing NeOH/CH₂Cl₂ 5%→10% yielded the amixture of 2′ and 3′ isomers; of the product as a dark oil (9.8 g).

Example 54 5′-O-Dimethoxytrityl-2′-O-pentyluridine

The mixture of 2′-O-pentyluridine and 3′-O-pentyluridine (9.8 g) wasreacted with dimethoxytrityl chloride (10.5 g) as per the procedure ofExample 51. The crude product was purified on a silica gel column (1000g). Elution with Hex.-EtOAc (3:1→1:1) gave 5.5 g of the 2′-O-pentylisomer and 3 g of the 3′-O-pentyl isomer. Anal. Calcd. forC₃₅H₃₇N₂O₈.½H₂O: C, 67.51; H, 6.55; N, 4.5. Found: C, 67.48; H, 6.55; N,4.5.

Example 55 5′-O-Dimethoxytrityl-2′-O-pentyluridine-3′-O-(β-cyanoethylN,N-diisopropylphosphormidite)

The protected 5′-O-dimethoxytrityl-2′-O-pentyluridine (4.6 g. 0.007 mol)was placed in a dry round bottom flask containing a teflon stir-bar. Theflask was purged with argon. Anhydrous methylene chloride was added tothe flask in an amount sufficient to dissolve the nucleoside. Previouslyvacuum dried N,N-diisopropylaminohydrotetrazolide (600 mg, 0.014 mol)was added under argon. Bis-N,N-diisopropylamino-cyanoethylphosphite (4.5g, 4.7 ml, 2 eq.) was added with, stirring via syringe. The reaction wasstirred under argon at 25° C. for 16 h. After verifying the completionof the reaction by TLC, the reaction was transferred to a separatoryfunnel and the reaction flask was rinsed with methylene chloride (2×50mL). The combined organic layer was washed 2× with sat'd aq. sodiumbicarbonate. The organic layer was dried over magnesium sulfate,evaporated and taken up in toluene containing 1% triethylamine. Theresulting phosphoramidite was purified by silica gel flashchromatography (300 g) and eluted with Hexanes/ethyl acetate (3:1→1:1containing 1% triethylamine). Selected fractions were combined,concentrated under reduced pressure and dried to yield 2.67 g ofproduct. as a white foam. ³¹P-NMR (CDCl₃, H₃PO₄ std.) showed the correctdiastereomers

Example 56 2′-O-Methyluridine

As per the procedure of Example 49, uridine (8.5 g) as treated withdibutyl tin oxide (8.2 g, 1 eq). The resulting 2′,3′-O-dibutylstannyleneuridine was treated with iodomethane (16 ml) at 42° C. as per Example 50to give a mixture of the 2′ and 3′ alkylated products (3.5 g) as a foam.

Example 57 5′-O-(4,4′-Dimethoxytriphenylmethyl)-2′-O-methyluridine

2′-O-Methyluridine (8.0 g, 0.031 mol) was evaporated under reducedpressure with pyridine (100 mL) to an oil. To the residue was added4,4′-dimethoxytriphenylmethyl chloride (DMT-Cl, 11.5 g, 0.34 mol) andpyridine (100 mL). The mixture was stirred at 25° C. for 1.5 h and thenquenched by the addition of methanol (10 mL) for 30 min. The mixture wasconcentrated under reduced pressure and the residue was chromatographedon silica gel (250 g), Elution with hexanes-ethyl acetatetriethylamine(80:20:1) and then ethyl acetate-triethylamine (99:1). The appropriatefractions were combined, evaporated under reduced pressure and dried at25° C./0.2 mmHg for 1 h to provide 17.4 g (100%) of tan foam; TLC purity98% (Rf 0.23, hexanes-ethyl acetate 4:1); PMR (DMSO) d 11.4 (H-N³), 7.78(H-6), 7.6-6.8 (Bz), 5.8 (H-1′), 5.3 (H-5′), 5.25 (HO-3′), 3.7(CH₃O-Bz), 3.4, (CH₃O-2′).

Example 585′-O-(4,4′-dimethoxytriphenylmethyl)-2′-O-Methyluridine-3′-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

The product was prepared as per Example 54 from the intermediate5′O-(4,4′-dimethoxytriphenylmethyl)-2′-O-methyluridine. Ethylacetate-hexanes-triethylamine (59:40:1) was used as the chromatographyeluent to give the product as a solid foam in 60% yield. TLC homogenousdiastereomers, Rf 0.58; 0.44 [ethyl acetate-hexanes-triethylamine59:40:1)). ³¹P-NMR (CDCl₃, H₃PO₄ std.) d 148.11; 148.61 (diastereomers).

Example 59 2′-O-Propyluridine

As per the procedure of Example 49, uridine (10 g) was treated withdibutyl tin oxide (10.2 g, 1 eq). The resulting2′,3′-O-dibutylstannylene uridine was treated with iodopropane (8 ml, 2eq.) at 110° C. as per Example 50 to give a mixture of the 2′ and 3′isomers (5.5 g) as a foam.

Example 60 5′-O-(4,4′-Dimethoxytriphenylmethyl)-2′-O-propyluridine

The mixture of 2′-O-propyluridine and 3′-O-propyluridine (3.6 g) wasreacted with dimethoxytrityl chloride (4.2 g, 1.0 eq.) as per Example51. The residue was chromatographed on silica gel eluted with Hex/EtOAc(1:1 with 1% triethylamine). The appropriate fractions were combined,evaporated under reduced pressure and dried to provide 4.2 g of a whitefoam. Anal. Calcd. for C₃₃H₃₆N₂O₈.½H₂O: C, 67.33; H, 6.16; N, 4.76.Found: C, 67.15; H, 6.24; N, 4.44.

Example 615′-O-(4,4′-dimethoxytriphenylmethyl)-2′-O-propyluridine-3′-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

The product was prepared as per Example 54 from the intermediate5′-O-(4,4′-dimethoxytrityl)-2′-O-propyluridine (470 mg) to yield theproduct as a foam (477 mg).

Example 62 2′-O-Nonyluridine

As per the procedure of Example 49, uridine (22.5 g) was treated withdibutyl tin oxide (22.5 g, 1 eq). The resulting2′,3′-O-dibutylstannyleneuridine was treated with iodononane (11 ml, 1.3eq.) at 130-140° C. as per Example 50 to give the 2′ and 3′ isomers(11.2 g) as an oil.

Example 63 5′-O-(4,4′-Dimethoxytriphenylmethyl)-2′-O-nonyluridine

The mixture of 2′-O-nonyluridine and 3′-O-nonyluridine (11.2 g) wasreacted with dimethoxytrityl chloride (10.5 g) as per Example 51. Theresidue was chromatographed on silica gel eluted with Hex/EtOAc (3:1→1:1with 1% triethylamine). The appropriate fractions were combined,evaporated under reduced pressure and dried to provide 5.2 g of a foam.An analytical sample was rechromatographed using toluene/EtOAc (3:1 with1% triethylamine) Anal. Calcd. for C₃₉H₄₈N₂O₈: C, 69.62; H, 7.19; N,4.16. Found: C, 69.66; H, 7.18; N, 4.06.

Example 645′-O-(4,4′-dimethoxytriphenylmethyl)-2′-O-nonyluridine-3′-O-(β-cyanoethylN,N-diisopropylphosphormidite)

The product was prepared as per Example 54 from the intermediate5′-O-(4,4′-dimethoxytrityl)-2′-O-nonyluridine (3.1 g) to yield theproduct as a foam (2.49 g).

Example 65 2′-O-Hexenyluridine

As per the procedure of Example 49, uridine (10.5 g) was treated withdibutyl tin oxide (10.5 g, 1 eq). The resulting2′,3′-O-dibutylstannyleneuridine was treated with 6-bromohexene (3.5 ml,1.2 eq.) and sodium iodide (3.3 g, 1.o eq.) at 115° C. as per Example 50to give the 2′ and 3′ isomers (3.3 g) as a foam.

Example 66 5′-O-(4,4′-Dimethoxytriphenylmethyl)-2′-O-hexanyluridine

The mixture of 2′-O-hexenyluridine and 3′-O-hexenyluridine (3.1 g) wasreacted with dimethoxytrityl chloride (3.5 g, 1.1 eq.) as per Example51. The residue was chromatographed on silica gel eluted with Hex/EtOAc(3:1→1:1 with 1% triethylamine). The appropriate fractions werecombined, evaporated under reduced pressure and dried to provide 2.3 gof a white foam. Anal. Calcd. for C₃₆H₄₀N₂O₈.½H₂O: C, 67.80; H, 6.48; N,4.39. Found: C, 68.77; H, 6.41; N, 4.45.

Example 675′-O-(4,4′-Dimethoxytriphenylmethyl)-2′-O-hezenyluridine-3′-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

The product is prepared as per Example 54 from the intermediate5′-O-(4,4′-dimethoxytrityl)-2′-O-hexenyluridine.

Example 685′-O-Dimethoxytrityl-2′-O-[hexyl-ω-(N-phtbalisido)]uridine-3′-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

In a like manner as per Examples 50 through 52, using N-(6-bromohexyl)phthalimide, an N-phthalimide substituted hexyl group was introduced atthe 2′-position of uridine followed by dimethoxytritylation andphosphitylation to give the title nucleotide.

Example 695′-O-Dimethoxytrityl-2-O-[decyl-ω-(N-phthalimido)]uridine-3-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

In a like manner as per Examples 50 through 52, usingN-(10-bromodecyl)phthalimide, an N-phthalimide substituted decyl groupwas introduced at the 2′-position of uridine followed bydimethoxytritylation and phosphitylation to give the title nucleotide.

Example 70 N4-Bensoyl-2′-O-methylcytidine, Method A

Step 1. 3′,5′-O-[(1,1,3,3-Tetraisapropyl)-1,3-disiloxanediyl]cytidine

With stirring, cytidine (40 g, 0.165 mol) and1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (TIPS-Cl, 50 g, 0.159 mol)were added to dry pyridine (250 mL). After stirring for 16 h at 25° C.,the reaction was concentrated under reduced pressure to an oil. The oilwas dissolved in methylene chloride (800 mL) and washed with sat'dsodium bicarbonate (2×300 mL). The organic layer was passed through asilica gel (200 g) scrub column. The product was recovered by elutionwith methylene chloride-methanol (97:3). The appropriate fractions werecombined, evaporated under reduced pressure and dried at 25° C./0.2 mmgfor 1 h to give 59.3 g (77%) of oil. TLC purity 95% (Rf 0.59, ethylacetate-methanol 9:1). The product may be crystallized from ethylacetate as white crystals, mp 242-244° C. 41 PMR (DMSO) d 7.7 (H-6),5.68 (H-5), 5.61 (HO-2′), 5.55 (H-1′).

Step 2.N4-Benzyl-3′-5′-O-[(1,1,3,3)tetraisopropyl-1,3-disiloxanediyl]cytidine

Benzoyl chloride (18.5 g, 0.13 mol) was added over 30 min to a stirredsolution of 3′,5′-O-[(1,1,3,3-tetraisopropyl)1,3-disiloxanediyl]cytidine(58 g, 0.12 mol) and triethylamine (15.6 g, 0.16 mol) indimethylacetamide (400 mL) at 5° C. The mixture was allowed to warm to25° C. for 16 h and then poured onto ice water (3.5 L) with stirring.The resulting solid was collected, washed with ice water (3×500 mL) anddried at 45° C./0.2 mmHg for 5 h to provide 77 g (100%) of solid. TLCpurity ca. 90% (Rf 0.63, chloroform-methanol 9:1); PMR (CDCl₃) d 8.32(H-6); mp 100-101° C.

step 3.N4-Benzoyl-2′-O-methyl-3′,5′-O-(1,1,3,3)tetraisopropyl-1,3-disiloxanediyl]cytidine

A mixture ofN4-benzoyl-3′-5′-O-[(1,1,3,3)tetraisopropyl-1,3-disiloxanediyl]cytidine(166 g, 0.25 mol, 90% purity), silver oxide (150 g, 0.65 mol) andtoluene (300 mL) was evaporated under reduced pressure. More toluene(500 mL) was added and an additional amount (100 mL) was evaporated.Under a nitrogen atmosphere, methyl iodide was added in one portion andthe reaction was stirred at 40° C. for 16 h. The silver salts werecollected and washed with ethyl acetate (3×150 mL). The combinedfiltrate was concentrated under reduced pressure. The residue wasdissolved in a minimum of methylene chloride, applied to a silica gelcolumn (1 kg) and eluted with hexanes-ethyl acetate (3:2→1:1). Theappropriate fractions were combined, concentrated under reduced pressureand dried at 45° C./0.2 mmHg for 1 h to yield 111 g (66%) of oil; TLCpurity ca. 90% (Rf 0.59, hexanes-ethyl acetate 3:2). PMR (CDCl₃) d 8.8(br s, 1, H-N⁴), 8.40 (d, 1, H-6), 8.0-7.4 (m, 6, H-5 and Bz), 5.86 (s,1, H-1′), 3.74 (s, 3, CH₃O-2′).

Step 4. N4-Benzoyl-2′-O-methylcytidine

A solution ofN4-benzoyl-2′-O-ethyl-3′,5′-O-[(1,1,3,3)tetraisopropyl-1,3-disiloxanediyl]cytidine(111 g, 0.18 mol) in methanol (160 mL) and tetrahydrofuran (640 mL) wastreated with tetrabutylammonium fluoride solution (368 mL, 1 M intetrahydrofuran). The reaction was stirred at 25° C. for 16 h. The pHwas adjusted to 7 with Amberlite IRC-50 resin. The mixture was filteredand the resin was washed with hot methanol (2×200 mL). The combinedfiltrate was concentrated under reduced pressure, absorbed on silica gel(175 g) and chromatographed on silica gel (500 g, ethyl acetate-methanol19:1→4:1). Selected fractions were combined, concentrated under reducedpressure and dried at 40° C./0.2 mmHg for 2 h to yield 28 g (42.4%,21.5% from cytidine) of solid; TLC homogenous (Rf 0.37, ethyl acetate).mp 178-180° C. (recryst. from ethanol); PMR (CDCl₃) d 11.22 (br s, 1,H-N⁴), 8.55 (d, 1, H-6), 8.1-7.2 (m, 6, H-5 and Bz), 5.89 (d, 1, H-1′),5.2 (n, 2, HO-3′,5′), 3.48 (s, 3, CH₃O-2′).

Example 71 N4-Benzoyl-2′-O-methylcytidine, Method B

Step 1. 2′-O-methylcytidine

Cytidine (100 g, 0.41 mol) was dissolved in warm dimethylformamide (65°C., 1125 mL). The solution was cooled with stirring to 0° C. A slow,steady stream of nitrogen gas was delivered throughout the reaction.Sodium hydride (60% in oil, washed thrice with hexanes, 18 g, 0.45 mol)was added and the mixture was stirred at 0° C. for 45 min. A solution ofmethyl iodide (92.25 g, 40.5 mL, 0.65 mol) in dimethylformamide (400 mL)was added in portions over 4 h at 0° C. The mixture was stirred for 7 hat 25° C. and then filtered. The filtrate was concentrated to drynessunder reduced pressure followed by co-evaporation with methanol (2×200mL). The residue was dissolved in methanol (350 mL). The solution wasadsorbed on silica gel (175 g) and evaporated to dryness. The mixturewas slurried in dichloromethane (500 mL) and applied on top of a silicagel column (1 kg). The column was eluted with a gradient ofdichloromethane-methanol (10:1→2:1). The less polar 2′,3′-dimethyl sideproduct was removed and the coeluting 2′ and 3′-O-methyl productcontaining fractions were combined and evaporated under reduced pressureto a syrup. The syrup was dissolved in a minimum of hot ethanol (ca. 150mL) and allowed to cool to 25° C. The resulting precipitate (2′lesssoluble) was collected, washed with ethanol (2×25 ml) and dried to give15.2 g of pure 2′-O-methylcytidine; mp 252-254° C. mp 252-254° C.) ; TLChomogenous (Rf 0.50, dichloromethane-methanol 3:1, (Rf of 3′ isomer 0.50and the dimethyl product 0.80). The filtrate was evaporated to give 18 gof a mixture of isomers and sodium iodide.

Stop 2. N4-Benxoyl-2′-O-methylcytidine

The pure 2′-O-methylcytidine (15.2 g, 0.060 mol) was dissolved in asolution of benzoic anhydride (14.7 g, 0.12 mol) in dimethylformamide(200 mL). The solution was stirred at 25° C. for 48 h and thenevaporated to dryness under reduced pressure. The residue was trituratedwith methanol (2×200 mL), collected and then triturated with warm ether(300 mL) for 10 min. The solid was collected and triturated with hot2-propanol (50 mL) and allowed to stand at 4° C. for 16 h. The solid wascollected and dried to give 17 g of product. The crude filtrate residue(18 g) of 2′-O-methylcytidine was treated with benzoic anhydride (17.3g, 0.076 mol) in dimethylformamide (250 mL)-as above and triturated in asimilar fashion to give an additional 6.7 g of pure product for a totalyield of 23.7 g (16% from cytidine) of solid; TLC homogenous; (Rf 0.25,chloroform-methanol 5:1, co-spots with material made utilizing Method A)

Example 72N4-Benzoyl-5′-O-(4,4′-dimethoxytriphenylmethyl)-2′-O-methylcytidine

N4-Benzoyl-2′-O-methylcytidine, (28 g, 0.077 mol) was evaporated underreduced pressure to an oil with pyridine (400 mL). To the residue wasadded 4,4′-dimethoxytriphenylmethyl chloride (DMT-Cl, 28.8 g, 0.085 mol)and pyridine (400 mL). The mixture was stirred at 25° C. for 2 h andthen quenched by the addition of methanol (10 mL) for 30 min. Themixture was concentrated under reduced pressure and the residue waschromatographed on silica gel (500 g, hexanes-ethyl acetatetriethylamine60:40:1 and then ethyl acetate-triethylamine 99:1). The appropriatefractions were combined, evaporated under reduced pressure and dried at40° C./0.2 mmHg for 2 h to give 26 g (74%) of foam; TLC homogenous (Rf0.45, ethyl acetate); PMR (DMSO) d 11.3 (H-N⁴), 8.4-6.9 (H-6, H-5, Bz),5.95 (H-1′), 5.2 (HO-3′), 3.7 (s, 6, CH₃O-trit.), 3.5 (s, 3, CH₃O-2′)

Example 73 N4-Benzoyl-5′-O-(4,4′-dimethoxytriphenylmethyl)-2′-O-methylcytidine-3′-O-(β-cyanoethyl N,N-diisopropylphosphoramidite)

The product was prepared as per the procedure of Example 38 startingwith intermediate compoundN4-benzoyl-5′-(4,4′-dimethoxytriphenylmethyl)-2′-O-methylcytidine (22.0g, 0.0333 mole) and using ethyl acetate-hexanes-triethylamine (59:40:1)as the chromatography eluent to give the product as a solid foam (23.6g) in 83% yield; TLC homogenous diastereomers (Rf 0.46; 0.33, ethylacetate-hexanestriethylamine 59:40:1); ³¹P-NMR (CD₃CN, H₃PO₄ std.) d150.341; 151.02 (diastereomers).

Example 74 2′-O-Nonylcytidine

Cytidine (10.1 g, 0.0415 mol), sodium hydride (2.0 g, 1.2 eq),iodononane (9.8 ml, 1.2 eq.) in DMF (100 ml) were reacted as per theprocedure of Example 71, Step 1 to yield the 2′ and 3′ isomers as asticky foam (11.6 g).

Example 75 N4-Benzoyl-2′-O-nonylcytidine

The mixture of 2′-O-nonylcytidine and 3′-nonylcytidine (11.5 g) isconverted to N4-benzoyl-2′-O-nonylcytidine as per the procedure ofExample 71, Step 2.

Example 76 N4-Benzoyl-5′-O-(dimethoxytrityl)-2′-O-nonylcytidine

N4-Benzoyl-2′-O-nonylcytidine (2.67 g, 0.0056 mol) was treated withdimethoxytrityl chloride (2.0 g, 1.1 eq) as per the procedure of Example72 to give 4.2 g of pure product. Anal. Calcd. for C₄₆H₅₃N₃O₈.½H₂O: C,70.39; H, 6.93; N, 5.35. Found: C, 71.20; H, 6.88; N, 5.41.

Example 77N4-Benzoyl-5′-O-(dimethoxytrityl)-2′-O-nonylcytidine-3′-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

The product was prepared as per the procedure of Example 38 startingwith intermediate compoundN4-benzoyl-5′-(4,4′-dimethoxytriphenylmethyl)-2′-O-nonylcytidine (4.1 g,0.0053 mole) treated with bis-N,N-diisopropylaminocyanoethylphosphite(3.3 ml) and N,N-diisopropylaminohydrotetrazolide (450 mg). The productwas eluted from the silica gel column using Hexane/EtOAc (3:1→1:1 with1% triethylamine) as the chromatography eluent to give the product as asolid foam (4.21 g). ³¹P-NMR (CD₃CN, H₃PO₄ std.) shows thediastereomers;

Example 78 2′-O-Pentylcytidine

Cytidine (10 g, 0.041 mol), sodium hydride (2.4 g, 1.5 eq), bromopentane(7.6 ml, 1.5 eq.) in DMSO (90 ml) were reacted as per the procedure ofExample 71, Step 1 to yield the 2′ and 3′ isomers as a foam (7.6 g).

Example 79 N4-Benzoyl-2′-O-pentylcytidine

The mixture of 2′-O-pentylcytidine and 3′-O-pentylcytidine (7.5 g) isconverted to N4-benzoyl-2′-O-pentylcytidine as per the procedure ofExample 71, Step 2.

Example 80 N4-Benzoyl-5′-O-(dimethoxytrityl)-2′-O-pentylcytidine

N4-Benzoyl-2′-O-pentylcytidine (3.0 g, 0.007 mol) was treated withdimethoxytrityl chloride (2.7 g, 1.1 eq) as per the procedure of Example72 to give 3.5 g of pure product. Anal. Calcd. for C₄₂H₄₅N₃O₈.½H₂O: C,69.21; H, 6.36; N, 5.76. Found: C, 69.51; H, 6.30; N, 5.71.

Example 81N4-Benzoyl-5′-O-(dimethoxytrityl)-2′-O-pentyloytidine-3′-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

The product was prepared as per the procedure of Example 38 startingwith intermediate compoundN4-benzoyl-5′-O-(4,4′-dimethoxytriphenylmethyl)-2′-O-pentylcytidine (3.5g, 0.0048 mole) treated with bis-N,N-diisopropylaminocyanoethylphosphite(2.9 g, 3.1 ml, 2 eq.) and N,N-diisopropylaminohydrotetrazolide (400 mg,0.5 eq.). The product was eluted from the silica gel column usingHexane/EtOAc (3:1→1:1 with 1% triethylamine) as the chromatographyeluent to give the product as a solid foam (3.24 g). ³¹P-NMR (CD₃CN,H₃PO₄ std.) shows the diastereomers.

Example 82 2′-O-Propylaytidine

Cytidine (16.5 g, 0.068 mol) was treated with sodium hydride (4.5 g) andbromopropane (15 ml) in DMF (150 ml) at room temperature for three days.The resulting reaction mixture was used directly in the next step (seeExample 83).

Example 83 N4-Benzoyl-2′-O-propylcytidine

To the 2′-O-propylcytidine reaction mixture of Example 82 in an ice bathwas added pyridine (60 ml) and trimethylsilIyl chloride (60 ml). Thereaction was stirred for 30 mins followed by the addition of benzoylchloride (55 ml). The resulting reaction mixture was stirred for 2.5 hr.and then cooled in an ice bath. H₂O (100 ml) and conc. NH₄OH (100 ml)were added. After stirring for 30 mins, the reaction mixture wasevaporated and the residue partition between H₂O and CH₂Cl₂. The organicphase was washed once with dil Na₂CO₃, once with dil HCl, dried overMgSO₄ and evaporated. The resulting residue was loaded on a silica gelcolumn (150 g) and eluted with first CH₂Cl₂ then 5 to 10% MeOH in CH₂Cl₂as the elution solvent. The product containing fractions were evaporatedto a foam. The foam was crystallized from EtOAc/Hexanes to give theproduct (6.5 g total) in several crystal batches.

Example 84 N4-Benzoyl-5′-O-(dimethoxytrityl)-2′-O-propylcytidine

N4-Benzoyl-2′-O-propylcytidine (3.0 g, 0.007 mol) was treated withdimethoxytrityl chloride (1.5 g) as per the procedure of Example 72 togive 1.5 g of pure product. Anal. Calcd. for C₄₀H₄₂N₃O₈.½H₂O: C, 68.45;H, 6.18; N, 5.99. Found: C, 68.39; H, 5.99; N, 5.95.

Example 85N4-Benzoyl-5′-O-(dimethoxytrityl-2′-O-propylcytidine-3′-O-(β-cyanoethylN,N-diisopropylphosphoramidite)

The product was prepared as per the procedure of Example 38 startingwith intermediate compoundN4-benzoyl-5′-O-(4,4′-dimethoxytriphenylmethyl)-2′-O-propylcytidine (3.8g, 0.0055 mole) treated with bis-N,N-diisopropylaminocyanoethylphosphite(3.5 ml, 2 eq.) and N,N-diisopropylaminohydrotetrazolide (500 mg, 0.5eq.). The product was eluted from the silica gel column usingHexane/EtOAc (1:1 with 1% triethylamine) as the chromatography eluent togive the product as a solid foam (4.72 g) ³¹P (CD₃CN, H₃PO₄ std.) showsthe diastereomers.

Example 86N2,N6-Diisobutyrylamino-9-(2′-O-ethyl-β-D-ribofuranosyl)purine

N2, N6-Diamino-9-(2′-O-methyl-β-D-ribofuranosyl) purine (1.6 g, 5.39mmol, see Example 34) was co-evaporated with pyridine (25 ml). Asuspension of the residue in pyridine (410 ml) was cooled in an ice bathand trimethylsilyl chloride (4.8 ml) was added. The reaction mixture wasstirred for 30 mins followed by the addition of butyryl chloride (2.8ml, 5 eq). The resulting reaction mixture was stirred at roomtemperature for 4 hours. H₂O (10 ml) and conc. NH₄OH (10 ml) were addedwith stirring to quench the reaction mixture. After 30 mins, thereaction mixture was evaporated and the residue purified on a silica gelcolumn using CH₂Cl₂→10% MeOH/CH₂Cl₂ to elute the product. Theappropriate fractions were evaporated to yield the product as an oil(2.4 g).

Example 87N2,N6-Diisobutyrylamino-9-(5′-O-dimethoxytrityl-2′-O-methyl-β-D-ribofuranoxyl)purine

N2,N6-Diisobutyrylamino-9-(2′-O-methyl-β-D-ribofuranosyl)purine (2.4 g)was co-evaporated with pyridine and redissolved in pyridine.Dimethoxytrityl chloride (1.8 g, 1 eq) and dimethylaminopyridine (5 mg)were added and the resulting solution was stirred overnight at roomtemperature. The solvent was partly evaporated and the residue partitionbetween CH₂Cl₂—dil. Na₂CO₃. The organic phase was washed with dil.Na₂CO₃, dried with NgSO₄ and evaporated. The residue was purified on asilica gel column eluted with Hexanes/EtOAc (1:1) containing 1%triethylamine. The fraction contain the product were evaporated to yieldthe product as a foam (2.4 g).

Example 88N2,N6-Diisobutyrylamino-9-[5′-O-dimethoxytrityl-2′-O-methyl-3′O-(β-cyanoethylN,N-diisopropylphosphoramide)-β-D-ribofuranosyl]purine

N2,N6-Diisobutyrylamino-9-(5′-O-dimethoxytrityl-2′-O-methyl-β-D-ribofuranosyl)purine(1.7 g, 0.0023 mol) was treated withbis-N,N-diisopropylaminocyanoethylphosphite (1.48 ml, 2 eq.) andN,N-diisopropylaminohydrotetrazolide (200 mg) at room temperatureovernight. The reaction mixture was partitioned between dil.Na₂CO₃/CH₂Cl₂, the organic phase was dried oiler MgSO₄ and evaporated.The residue was loaded on a silica gel column and eluted withHexanes/EtOAc (3:1→1:1 with 1% triethylamine) to give the product as asolid foam (1.73 g). ³¹P-NMR (CD₃CN, H₃PO₄ std.) shows thediastereomers.

Example 89 Oligonucleotide Synthesis

Once nucleoside phosphoramidites of the invention have been prepared,they can then subsequently be incorporated into oligonucleotides, whichare synthesized by a standard solid phase, automated nucleic acidsynthesizer such as the Applied Biosystems, Incorporated 380B orMilliGen/Biosearch 7500 or 8800. Standard phosphoramidite couplingchemistries (see, e.g., M. Caruthers, Oligonucleotides. AntisenseInhibitors' of Gene Expression., pp. 7-24, J. S. Cohen, ed., CRC Press,Inc. Boca Raton, Fla., 1989) are used with these synthesizers to providethe desired oliqonucleotides. The Beaucage reagent (see, e.g., J. Am.Chem. Soc. 1990, 112, 1253) or elemental sulfur (see, e.g., TetrahedronLetters 1981, 22, 1859), can likewise be used to providephosphorothioate oligonucleotidies.

We claim:
 1. A process for preparing an oligonucleotide that comprisesat least one 2′-O-alkylated cytidine nucleotide comprising: alkylating acytidine to form a 2′-O-alkylated cytidine; blocking the 5′-hydroxylmoiety of said 2′-O-alkylated cytidine; phosphitylating the 3′-positionof said 5′-blocked 2′′-alkylated cytidine to form a 2′-O-alkylatedcytidine 3′-O-phosphoramidite; and coupling said 2′-O-alkylated cytidine3′-O-phosphoramidite with a 5′-hydroxyl moiety on an oligonucleotideutilizing phosphoramidite coupling conditions.